I don’t think it’s a Fenix issue because it works correctly with the MSFS default pushback and the Fenix pushback…
How you'd expect GSX could possibly control what appears on the airplane own instrumentation, especially considering the bypass pin is not even a standard system provided by the simulator, so we could possibly have used a standard variable, even assuming the Fenix would have used that as well ( if it ever existed ), considering it's a plane with lots of custom code, even for systems that DO exists in MSFS ?
I haven't seen anything in the Fenix updates that suggest they have integrated any logic to interact with GSX and, in order to do something like you are expecting to see, that is the message about the steering pin matching *exactly* the moment where the GSX crew inserted/removed it, would require some custom code on Fenix part, and probably even a new variable published by GSX the airplane code can use, to be notified of exactly that situation.