I use XnViewMP 0.88 64bits on Debian GNU/Linux 9.3.
When I'm in Browser or in Fullscreen modes I can navigate to GPS tab (next to ExifTool) but there is nothing in the opened GPS tab. I can perform left-click on it and see 'Reload' pop-up message. That's all. Note that both 'Open GPS location in GeoHack...' and 'Open GPS location in Google Earth...' tools work for me.
I didn't use GPS feature for few months. But I remembered that it worked fine.
What I tried:
- different versions (from 0.84)
to remove .config/xnviewmp/ in my home directory
checked that XnViewMP isn't blacklisted in my firewall