Hmmm…further testing (I forgot I had firewalld active for some other testing)… now working as expected for me (openSUSE 15.1, NetworkManager version 1.10.6)…
My log for reference…
pr 06 12:39:04 linux-4k1z NetworkManager[1306]: <info> [1586133544.0817] audit: op="statistics" arg="refresh-rate-ms" pid=2067 uid=1000 result="success"
Apr 06 12:39:07 linux-4k1z NetworkManager[1306]: <info> [1586133547.2037] audit: op="connection-activate" uuid="f052500e-251a-4667-9935-160e4bb69c68" name="SKT VPN (PPTP)" pid=2067 uid=1000 result="success"
Apr 06 12:39:07 linux-4k1z NetworkManager[1306]: <info> [1586133547.2190] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",0]: Started the VPN service, PID 7724
Apr 06 12:39:07 linux-4k1z NetworkManager[1306]: <info> [1586133547.2459] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",0]: Saw the service appear; activating connection
Apr 06 12:39:07 linux-4k1z NetworkManager[1306]: <info> [1586133547.3085] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",0]: VPN plugin: state changed: starting (3)
Apr 06 12:39:07 linux-4k1z pppd[7734]: Plugin /usr/lib64/pppd/2.4.7/nm-pptp-pppd-plugin.so loaded.
Apr 06 12:39:07 linux-4k1z NetworkManager[1306]: Plugin /usr/lib64/pppd/2.4.7/nm-pptp-pppd-plugin.so loaded.
Apr 06 12:39:07 linux-4k1z pppd[7734]: pppd 2.4.7 started by root, uid 0
Apr 06 12:39:07 linux-4k1z pppd[7734]: Using interface ppp0
Apr 06 12:39:07 linux-4k1z NetworkManager[1306]: <info> [1586133547.3319] manager: (ppp0): new Ppp device (/org/freedesktop/NetworkManager/Devices/11)
Apr 06 12:39:07 linux-4k1z NetworkManager[1306]: Using interface ppp0
Apr 06 12:39:07 linux-4k1z NetworkManager[1306]: Connect: ppp0 <--> /dev/pts/1
Apr 06 12:39:07 linux-4k1z pppd[7734]: Connect: ppp0 <--> /dev/pts/1
Apr 06 12:39:07 linux-4k1z pptp[7737]: nm-pptp-service-7724 log[main:pptp.c:333]: The synchronous pptp option is NOT activated
Apr 06 12:39:07 linux-4k1z NetworkManager[1306]: Error: either "to" is duplicate, or "uid" is a garbage.
Apr 06 12:39:07 linux-4k1z pptp[7747]: nm-pptp-service-7724 log[ctrlp_rep:pptp_ctrl.c:258]: Sent control packet type is 1 'Start-Control-Connection-Request'
Apr 06 12:39:07 linux-4k1z pptp[7747]: nm-pptp-service-7724 log[ctrlp_disp:pptp_ctrl.c:758]: Received Start Control Connection Reply
Apr 06 12:39:07 linux-4k1z pptp[7747]: nm-pptp-service-7724 log[ctrlp_disp:pptp_ctrl.c:792]: Client connection established.
Apr 06 12:39:08 linux-4k1z pptp[7747]: nm-pptp-service-7724 log[ctrlp_rep:pptp_ctrl.c:258]: Sent control packet type is 7 'Outgoing-Call-Request'
Apr 06 12:39:08 linux-4k1z pptp[7747]: nm-pptp-service-7724 log[ctrlp_disp:pptp_ctrl.c:877]: Received Outgoing Call Reply.
Apr 06 12:39:08 linux-4k1z pptp[7747]: nm-pptp-service-7724 log[ctrlp_disp:pptp_ctrl.c:916]: Outgoing call established (call ID 0, peer's call ID 1470).
Apr 06 12:39:08 linux-4k1z pppd[7734]: CHAP authentication succeeded
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: CHAP authentication succeeded
Apr 06 12:39:08 linux-4k1z pppd[7734]: CCP terminated by peer (No compression negotiated)
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: CCP terminated by peer (No compression negotiated)
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: Compression disabled by peer.
Apr 06 12:39:08 linux-4k1z pppd[7734]: Compression disabled by peer.
Apr 06 12:39:08 linux-4k1z pppd[7734]: local IP address 192.168.3.194
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4685] device (ppp0): state change: unmanaged -> unavailable (reason 'connection-assumed', sys-iface-state: 'external')
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: local IP address 192.168.3.194
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: remote IP address 192.168.3.254
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: primary DNS address 172.31.200.6
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: secondary DNS address 208.67.222.222
Apr 06 12:39:08 linux-4k1z pppd[7734]: remote IP address 192.168.3.254
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4690] device (ppp0): state change: unavailable -> disconnected (reason 'none', sys-iface-state: 'external')
Apr 06 12:39:08 linux-4k1z pppd[7734]: primary DNS address 172.31.200.6
Apr 06 12:39:08 linux-4k1z pppd[7734]: secondary DNS address 208.67.222.222
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4781] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",0]: VPN connection: (IP4 Config Get) reply received from old-style plugin
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4786] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",12:(ppp0)]: Data: VPN Gateway: 124.157.82.246
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4786] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",12:(ppp0)]: Data: Tunnel Device: "ppp0"
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4786] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",12:(ppp0)]: Data: IPv4 configuration:
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4786] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",12:(ppp0)]: Data: Internal Address: 192.168.3.194
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4786] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",12:(ppp0)]: Data: Internal Prefix: 32
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4786] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",12:(ppp0)]: Data: Internal Point-to-Point Address: 192.168.3.254
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4787] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",12:(ppp0)]: Data: Static Route: 0.0.0.0/0 Next Hop: 0.0.0.0
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4787] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",12:(ppp0)]: Data: Static Route: 192.168.3.254/32 Next Hop: 0.0.0.0
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4787] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",12:(ppp0)]: Data: Internal DNS: 172.31.200.6
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4787] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",12:(ppp0)]: Data: Internal DNS: 208.67.222.222
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4787] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",12:(ppp0)]: Data: DNS Domain: '(none)'
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4787] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",12:(ppp0)]: Data: No IPv6 configuration
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.4821] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",12:(ppp0)]: VPN connection: (IP Config Get) complete
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: nisdomainname: you must be root to change the domain name
Apr 06 12:39:08 linux-4k1z NetworkManager[1306]: <info> [1586133548.8803] vpn-connection[0x55e29c4aa180,f052500e-251a-4667-9935-160e4bb69c68,"SKT VPN (PPTP)",12:(ppp0)]: VPN plugin: state changed: started (4)
Apr 06 12:39:09 linux-4k1z ip-up.d/10-netconfig[7755]: nisdomainname: you must be root to change the domain name
Apr 06 12:39:09 linux-4k1z ip-up.d/10-netconfig[7755]: nisdomainname: you must be root to change the domain name
Apr 06 12:39:09 linux-4k1z pppd[7734]: Script /etc/ppp/ip-up finished (pid 7751), status = 0x0
Apr 06 12:39:09 linux-4k1z NetworkManager[1306]: Script /etc/ppp/ip-up finished (pid 7751), status = 0x0
Apr 06 12:39:10 linux-4k1z NetworkManager[1306]: <info> [1586133550.5754] audit: op="statistics" arg="refresh-rate-ms" pid=2067 uid=1000 result="success"