If you send your setup to support@tyflow.com I can look into the NaN issue.
I'll look into why mass isn't working as well. Mass assignments in tyFlow work a little differently than other properties for a couple of reasons. Perhaps I forgot to adjust the Custom Properties operator to do the special handling the same way the Mass and PhysX Shape operator do.
Edit: I checked the Custom Properties mass assignments and they work fine. Make sure your Custom Properties mass-assigner operator is below any PhysX Shape operator, since PhysX Shape does its own mass override by default (which can be disabled, but is enabled by default).
I'll look into why mass isn't working as well. Mass assignments in tyFlow work a little differently than other properties for a couple of reasons. Perhaps I forgot to adjust the Custom Properties operator to do the special handling the same way the Mass and PhysX Shape operator do.
Edit: I checked the Custom Properties mass assignments and they work fine. Make sure your Custom Properties mass-assigner operator is below any PhysX Shape operator, since PhysX Shape does its own mass override by default (which can be disabled, but is enabled by default).