First I highly recommend the mod that is listed here (and in several posts above I believe).
The HSI has been broken since I believe the 12/22 update, and you are correct, the glideslope is not working. In this case, the issue has nothing to do with the GPS, it’s the HSI that’s not working. The HSI is Carenado’s own gauge I believe. True, they rely on the default GPS, or whatever modded one you have installed, but they do write some of their own gauges. Although, do RNAV approaches provide vertical guidance?
I didn’t know XPlane had it’s own GNS530? The only 530’s I’m aware of in that is the RXP addon you can purchase and I think someone else does the same thing. They are both based on the Garmin Trainer and are fully functional GNS530’s. I believe RXP is in the process of porting to MSFS, but are currently stuck because of Sandbox issues and their reliance on the Garmin Trainer. I might be wrong on that point. In any event, I don’t know what X-plane has to do with this discussion.
But, the above mod is EXCELLENT, and the developer is constantly improving it.