This is from a developer on another forum:
The mere fact a ReWire module is named “Transport” broke things in Cubase update 9.5.21. This now brings up the internal transport controls instead of opening the small ReWire setup window. Looks like menu actions are mapped by strings and hence this naming conflict arises. This kind of side effect should never happen, regardless how a ReWire instrument is named.
So this is defintely a bug with the latest Cubase update. Please open a ticket with their support and let them know the above (copy/paste). The more Cubase users do that, the more likely it will get fixed.