I was guessing something like that. You have already checked that the phone gets location on the Sailfish side of things, which rules out trouble with the GPS receiver etc.
There have been reports about GPS not working in Android App Support, e.g. this one, but also a comment about it working in the [Release notes] Finlayson 5.2.0.18 - Jolla Phone first - #6 by ahjolinna thread. There was a discussion about getting the local transport app of Tampere working, maybe this comment helps? (Context in the replied-to posts above that one.)
I’m afraid I don’t have much more to offer at the moment.
Your case seems different than the “GPS works only once” thread. If nothing in the links above helps you, I think you need to file a bug report. You can do that on the phone with the Bugger! app from Chum, which will automatically include important information and format the report according to a template.
You can also create a new topic on the web. There’s a drop-down for Category in the composer. Pick Bug report to get the template.