Are you using a null modem cable (crossover) as well as the Startech converter which sounds like it already has null modem function built in?

If so, you either need to see of you can disable null modem on Startech unit (I don't know if this is possible) or use a straight cable instead of null modem crossover. Alternatively a second null modem cable or crossover adaptor will sort, albeit intelligently.

Meridian owner since 1992
Prime & PSU, Focal Elear headphones, Roon (ROCK 8Gi5 NUC), Explorer 1 & 2, F80. 200/203, various Sonos (via Roon).