After cloning RAC to non-RAC, ORA-1548 when attempting to drop UNDOTBS2

After cloning an 11.2.0.4 2-node RAC to non-RAC database (ASM to ACFS) using RMAN DUPLICATE from backup, UNDOTBS2 cannot be dropped due to a rollback segment that is partly available. It is not possible to rollback, since the transaction is ACTIVE with DEAD flag. There are no partly available rollback segments in the source database, the cloning was performed with cluster_database=FALSE, undo_tablespace=UNDOTBS1 and recovery was successful on the clone, so unsure what went wrong. Several different RAC databases are being cloned using this process and only one of them consistently has this issue.

This is primarily a nuisance, since the clone is just a staging database with a lifespan of a few weeks between refreshes. Despite not being able to drop the unneeded undo tablespace, can still disable thread 2 and drop the thread 2 redo logs.

Looking for troubleshooting advice or ideas on how the cloning process could be corrupting this unused undo tablespace.

Regards,

Doug