Having done some testing, the bug seems to be triggered after entering the squad view of any squad through the avenger barracks ---> squad management for the first time after loading a save. Entering the geoscape returns the game to normal (no time passes while in the avenger), however, entering the geoscape before triggering the bug will not prevent the bug.

I can only trigger the bug when loading a few specific saves.
Two of my manual save games, as well as any manual saves I made to duplicate them, are bugged. Duplicate saves created and loaded before the bug is triggered are still bugged. Duplicate saves created and loaded after triggering/resolving the bug (by entering and exiting the geoscape), seem to no longer be bugged.
None of the autosaves I have tested were affected, even those related to the bugged saves.

Saves made while the bug was active, would revert game time back to when the bug first triggered, though the save would still show the game time as it was when saved. (Loading the game save would show the time would be 10:01 am, but once loaded the game time would be 9:50 am at the bottom right of the screen). I could no longer trigger the bug for these saves once loaded.

I just encountered this today when I got up from customizing in squad view to go get food and came back to something really frustrating. A chosen avenger defence mission triggered while I was away but when I briefly exited the deployment menu, the game immediately auto launched a covert ops ambush, and now the avenger defense mission is stuck on my world map view but unable to be selected. Just necroing this in case any one has ideas