I have a somewhat related issue. I hope it's okay to continue here...
In (rare) cases, when I request a gate after landing, I get the message, that the gate is already occupied. When I arrive at the gate I see what seems to be the default ground handling crew together with the GSX equipment. The default marshaller seems to be the one occupying the gate, lol.
It happens randomly, it seems. I see no pattern, really. The GSX stuff is standing in the correct position. It's just that the default ground handling isn't removed by GSX, it seems. If I restart coutl and request again, the default stuff goes away as expected.