I’m not sure whether it’s Discourse Shared Edits or the #wiki-posts feature, since both were enabled on this particular post to avoid one editor making others’ changes obsolete.
So one post with both wiki and shared edits enabled…
Editor A makes revision 55 and presses “Done”.
Editor B goes straight to the revision history to see changes. Revision count shows 54 / 55, but there is no way to access revision 55. Once editor B has made a change, it was against revision 54, effectively removing revision 55 entirely.
There is no way to circumvent this. Having multiple editors at once for a single post is not supported by the wiki mode, but shared edits seem to create this bug with wiki revisions. It would be nice to be able to use both (in the way that HedgeDoc does it), or to neutralize potential misfit between the two editing modes.
I think I’ve seen another aspect to this bug - but it might be unrelated.
When Shared Edits is turned on for a post, if it is edited too soon (within 20 seconds or so), then a clash seems to occur where only one or the other edits is saved. In other words, the Shared Edit functionality doesn’t actually kick in despite it appearing to be active. Things get very confusing if either author close and re-enter the post again, with edits appearing and disappearing.
If left alone for a while everything seems to sort itself out (albeit with loss of some content). Perhaps a brief 30 second lock of the posts when shared edits are turned on would prevent this?