I rebuild ^rINDEX using, as recommended, D ##class(%Library.RoutineIndex).RebuildIndex($NAMESPACE). That reduced the number of ^rINDEX entries with an empty Date Modified, the cause of the $RO error. However, this function is partially based on ^ROUTINE which in its turn had bogus entries, all of the type ^ROUTINE("ABC",0,"SIZE")=<some integer>. That’s all these routines contain. I killed these ^ROUTINE nodes and rebuilt ^rINDEX. No empty Date Modified.