Yes, it is like a caching issue.
I tried your test with the ~~NOCACHE~~ option. When the first user clicks edit for the second time the page that loads contains the corrections of the second user!!!! IT WORKS :))))
How can I apply this to all pages? Before posting here I tried to set the option "Maximum age for cache (sec)" to be "-1" but I didn't get any results.
I'll try again.
Taggic wrote
sounds like a caching issue.
Assumption:
The click on Edit does not reload the original page source file but is working with a local cached copy
(until some timeout enforces to reload).
Just for a small test:
could you put a ~~NOCACHE~~ on that page and retry your steps ? I'm not sure if the nocache works in case of edit.
If it works it will not be the solution due to putting a nocahce on all pages would not make me happy.
But we may get a bit closer to the root cause.