Comment 7 for bug 1595837

The only way here is to update sqlalchemy to a higher version to catch original exception which is currently being interrupted by exception during attempt to do rollback. To be more precise, this fix will help with further investigations which is in sqlalchemy==1.0.12:

https://bitbucket.org/zzzeek/sqlalchemy/commits/8a1e619fb20df1be6ad2e0c563e451e17eb17628#chg-lib/sqlalchemy/util/langhelpers.py