root@Tower:~# ls -alF /boot/config/
total 584
drwx------ 11 root root 4096 Sep 4 12:08 ./
drwx------ 8 root root 4096 Jan 1 1970 ../
-rw------- 1 root root 256 Sep 4 11:41 Basic.key
-rw------- 1 root root 256 Sep 4 11:42 Plus.key
-rw------- 1 root root 256 Sep 4 11:42 Pro.key
-rw------- 1 root root 256 Sep 4 11:41 Trial.key
-rw------- 1 root root 3545 Sep 4 11:42 disk.cfg
-rw------- 1 root root 11265 Sep 4 11:42 disk.cfg.bak
-rw------- 1 root root 2650 Sep 4 11:42 disk.old
-rw------- 1 root root 427 Sep 4 11:41 docker.cfg
-rw------- 1 root root 288 Sep 4 11:41 domain.cfg
(file listing for clarity)
Same issue, removed the files Trial.key , Basic.key , Plus.key and the "Replace key" button emerged (refresh view) after which replacement had no issues. There is definitely a bug in the license validation / lifecycle management.
(files presumably are leftovers from years of license upgrades, however this only became a issue now, presumably due to either a keyfile counter > 3 , last replacement during Plus had no issues)
Ticket opened with support.