So the problem is that if room chain generator is started more than once in single generation request - which it occasionally is since there's (hard) for loop in BoardGenerator.cs 's BuildLevel coroutine calling RunGenerators() checking its return value - you initialize starting conditions (location and start room) again - which is not in sync with whatever current data was being generated so far (including them in the 2nd run would be probably incorrect anyway), so the generated layout breaks (despite chain being found correctly internally)
(I at first thought that the coroutine starting twice with combination with editor button click would be the problem, but 'decoroutining' it didn't help)
You might want to fix this properly - ( a quick fix directly in roomchain generator assigning initial location/room only on '1st' run is not stable, running out of iterations often. - The rooms seems to be generated OK if it passes, though, with Exists assignments being left as originally were)
Hope this helps, cheers!