I stopped using the calendar because this was happening in our group as well. I didn't want to take the time to sort it out. The first time I thought it was my error as I never used Calendar option before. The second time it happened I thought maybe I had incorrectly set the time zone. The third time I double and triple checked everything before posting the event. That was the last straw. After searching GIO, I didn't see where anyone else had reported it. I chalked it up to something weird and not worth my time to explore. Switched to using my personal calendar to generate a post to the group.
I watched your recording and was relieved to learn I am not alone.
ASG Volunteers Group.