If I try to edit a post which I have just created, I get the following error:
That post was edited by another user and your changes can no longer be saved
eg:
The “Save Edit” button also renames itself to “Overwrite Edit”.
This has only started happening since I updated on Friday to “2.8.0.beta2” ( 4681c670c0 )
If it helps, I update weekly, so this is a new issue which has appeared between Friday 4th June 2021 and Friday 11th June 2021.
It happens here on meta too (as per my screen shot).
I cannot work out the pattern to it. It does not happen every time, just sometimes 
Several of our users have reported this too.