I have posted a Ticket #117132: "Editing same profile data on two different computers causes failure!" at 12th May 2020 and got your answer "Thank you for contacting Geni. Thank you for also reporting the issue you came across regarding the same profile being edited by two different users at the same time. I was able to reproduce the issue and I have forwarded this to our engineers to investigate it further." but the error still exists today!
This is my description of the problem: On my laptop with win10 and chrome browser I opened in geni.com a profile and in Overview tab clicked Edit, and in the beginning of text added text 'Test 1'. Then I left laptop and did the same on my desktop computer (win10 and chrome browser) except wrote 'Test 2' in edit mode. Then I clicked 'save' on desktop, and update went ok, text 'Test 2' on screen. Then I switched to my laptop and clicked 'save' there. On laptop screen I see text 'Test 1' in overview. Then I press F5 (refresh) on my desktop and on the screen comes text 'Test 1' instead of 'Text 2'.
So, if two users happens to edit the same profile data at the same time, the result is random, the user who clicks 'save' as last one get the edit saved and the first one loses it. Not good! I know that this case can be very rare but in Facebook forum 'Yhteiset sukujuuret - sukututkimus nykypäivän työkaluin' I see a case this was happening. You can test it and repeat what I descibed. Look's like you have missed to lock the record when it is opened for editing for the first user, and the second user opening the same record should get message 'locked for update for one other user'.