Next time please capture and provide binary dump (tcpdump -w capture-file …), not default text summary. It allows looking at package details beyond what is shown by default.
Anyway, assuming 192.168.111.101 is grub2 client and 192.168.111.1 is HTTP server - client receives data from server up to approximately 11MB and then it stops accepting data due to no buffer space (TCP window becomes zero) and it never recovers.
13:15:24.009354 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11117227, win 65535, length 0
13:15:24.009355 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11120147, win 64804, length 0
13:15:24.009386 IP 192.168.111.1.443 > 192.168.111.101.1790: Flags [P.], seq 11176922:11179842, ack 1762, win 63987, length 2920
13:15:24.009393 IP 192.168.111.1.443 > 192.168.111.101.1790: Flags [P.], seq 11179842:11182762, ack 1762, win 63987, length 2920
13:15:24.021708 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11123067, win 61884, length 0
13:15:24.021777 IP 192.168.111.1.443 > 192.168.111.101.1790: Flags [P.], seq 11182762:11184951, ack 1762, win 63987, length 2189
13:15:24.041953 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11125987, win 58964, length 0
13:15:24.052069 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11127445, win 57506, length 0
13:15:24.072259 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11130365, win 54586, length 0
13:15:24.092444 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11133285, win 51666, length 0
13:15:24.112671 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11136205, win 48746, length 0
13:15:24.132850 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11137665, win 47286, length 0
13:15:24.153041 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11142045, win 42906, length 0
13:15:24.173291 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11144965, win 39986, length 0
13:15:24.193438 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11147885, win 37066, length 0
13:15:24.213681 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11150805, win 34146, length 0
13:15:24.223800 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11151532, win 33419, length 0
13:15:24.243983 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11154452, win 30499, length 0
13:15:24.264149 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11157372, win 27579, length 0
13:15:24.284361 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11160292, win 24659, length 0
13:15:24.304532 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11163212, win 21739, length 0
13:15:24.324759 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11166132, win 18819, length 0
13:15:24.341970 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11168376, win 16575, length 0
13:15:24.362149 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11171296, win 13655, length 0
13:15:24.382367 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11174216, win 10735, length 0
13:15:24.392444 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11174541, win 10410, length 0
13:15:24.412634 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11176922, win 8029, length 0
13:15:24.432869 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11179842, win 5109, length 0
13:15:24.453033 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11182762, win 2189, length 0
13:15:24.473277 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11184951, win 0, length 0
13:15:25.372035 IP 192.168.111.1.443 > 192.168.111.101.1790: Flags .], ack 1762, win 63987, length 0
13:15:25.380336 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11184951, win 0, length 0
13:15:27.164046 IP 192.168.111.1.443 > 192.168.111.101.1790: Flags .], ack 1762, win 63987, length 0
13:15:27.166143 IP 192.168.111.101.1790 > 192.168.111.1.443: Flags .], ack 11184951, win 0, length 0
13:15:30.780047 IP 192.168.111.1.443 > 192.168.111.101.1790: Flags .], ack 1762, win 63987, length 0
13:15:37.948133 IP 192.168.111.1.443 > 192.168.111.101.1790: Flags .], ack 1762, win 63987, length 0
13:15:52.284117 IP 192.168.111.1.443 > 192.168.111.101.1790: Flags .], ack 1762, win 63987, length 0
This matches error code (out of resources). It is impossible to decide whether this is due to firmware or grub bug (it is possible that grub stops processing new data for some reasons).
As the patch to use firmware HTTP(S) services is SUSE specific, you should open bug report on https://bugzilla.opensuse.org (same user/password as here). Attach binary tcpdump capture, provide as much details as possible (in particular, exact sizes of linux kernel and initrd are certainly interesting), do not forget to describe your setup, IP addresses of client and server etc.
As a workaround you may try to generate smaller initrd or test different boot protocol (HTTP, FTP, TFTP). Do you really needs encryption?