We need to do a full offline reindex to gerrit, to try and prevent T152640 recurring.
The reason why we had that problem was because the account index was not created which thus caused the logging in problems.
2.14.2 (when released) will fix this issue by looking directly at source and not in the index.
See discussion at https://groups.google.com/forum/#!topic/repo-discuss/_5iJcIsIa2Y
Another user reported the same problem as T152640 and did a full reindex after getting that error which fixed it for them.
Luca discovered gerrit starts even if the account index is not created which thus leads to errors like T152640