Found the following error messages:
**3400G:~ #** journalctl -b -2 -u btr* --no-pager
-- Logs begin at Sat 2021-02-27 11:52:04 CET, end at Sun 2048-05-10 00:31:44 CEST. --
Mar 01 06:23:44 3400G systemd[1]: Started Watch /etc/sysconfig/btrfsmaintenance.
Mar 01 06:23:44 3400G systemd[1]: **btrfs-balance.timer: Not using persistent file timestamp Sun 2048-05-10 00:31:16 CEST as it is in the future.**
Mar 01 06:23:44 3400G systemd[1]: Started Balance block groups on a btrfs filesystem.
Mar 01 06:23:44 3400G systemd[1]: **btrfs-scrub.timer: Not using persistent file timestamp Sun 2048-05-10 00:31:16 CEST as it is in the future.**
Mar 01 06:23:44 3400G systemd[1]: Started Scrub btrfs filesystem, verify block checksums.
Mar 01 06:23:44 3400G systemd[1]: **btrfs-trim.timer: Not using persistent file timestamp Sun 2048-05-10 00:31:16 CEST as it is in the future.**
Mar 01 06:23:44 3400G systemd[1]: Started Discard unused blocks on a mounted filesystem.
Mar 01 06:42:50 3400G systemd[1]: btrfs-balance.timer: Succeeded.
Mar 01 06:42:50 3400G systemd[1]: Stopped Balance block groups on a btrfs filesystem.
Mar 01 06:42:50 3400G systemd[1]: btrfs-scrub.timer: Succeeded.
Mar 01 06:42:50 3400G systemd[1]: Stopped Scrub btrfs filesystem, verify block checksums.
Mar 01 06:42:50 3400G systemd[1]: btrfs-trim.timer: Succeeded.
Mar 01 06:42:50 3400G systemd[1]: Stopped Discard unused blocks on a mounted filesystem.
Mar 01 06:42:51 3400G systemd[1]: btrfsmaintenance-refresh.path: Succeeded.
Mar 01 06:42:51 3400G systemd[1]: Stopped Watch /etc/sysconfig/btrfsmaintenance.
**3400G:~ #**
Fixed time stamps of files in /var and booted again:
**3400G:~ #** journalctl --list-boots
-5 abd4fae3a0d7467189c6c662d5696682 Sat 2021-02-27 11:52:04 CET—Sat 2021-02-27 11:55:18 CET
-4 615cea9929144231a7f0c1c802ae2fb4 Sun 2021-02-28 11:59:34 CET—Sun 2021-02-28 12:11:10 CET
-3 ac0f01f46e38483797faac13144d09b5 Sun 2021-02-28 12:11:25 CET—Sun 2021-02-28 13:40:17 CET
-2 32bc06d9ccd5423385e1c04aa44e7e32 Mon 2021-03-01 06:23:41 CET—Mon 2021-03-01 06:42:51 CET
-1 f3cc99abb140418fb8daf158db981afb Mon 2021-03-01 06:43:07 CET—Mon 2021-03-01 06:44:21 CET
0 8cdf71de1aeb471fbc8172d2294439f0 Sun **2048-05-10** 00:31:13 CEST—Sun 2048-05-10 00:31:44 CEST
**3400G:~ #**
Messages are now gone but system still claims wrong date for current boot. Any idea?