I tried doing the expand and then changing the system name, the password, set ssh and vnc, set the timezone to Denver, and connected to my wifi. GPSMON was still working. Rebooted and GPSMON was still working. This on a pi3b+ and a pi4.
Do you have an old or new DRAWS hat? The old ones have the gps port next to the radio ports. The new ones have the port on the end of the card.
When GPSMON is broken what does aplay -l show?
You might try commenting out the dtoverlay= line in /boot/config.txt.
Let me know what you find.
73 - Frank - K0FEI