As in the attached video file. This certainly doesn’t happen most of the time for most characters; it seems to be occasional and maybe character-specific.
Simply, the “Wait Turn” button is disabled at the start of a character’s turn, but becomes enabled after opening and closing the character screen.
I didn’t get the logs after exiting the game, but I can get them after it next happens, if that would be helpful.
I notice this sometimes also, but it’s not that the button is disabled, but rather the highlight is greyed out. You can still click on the Wait Turn button to wait.
Attached log from another reproduction. It seems to happen just to the character Humbert, and only in the first round of combat. He’s a superstitious wildman who starts combat at confident morale and has a missing nose.