Location is not detected via a recommended app

The app VRN eTarif, version 1.9.25 (com.sevenre.linear_v3145753.apk) is listed in /e/ Application Checker, but in version 1.4.0. I downloaded and installed it via APPS (foundation.e.apps / cleanapk.org).
Unfortunately, I am now unable to purchase a ticket. The “location” setting is enabled, everything works fine. The database has been updated: 7965 stops. ONLY: the stop where you are standing is not found, although you can see the current time in the Android settings (location - VRN etarif - last access).
With other apps (DB Navigator, stadtmobil, OsmAnd, Magic Earth) the display of the location works without problems.
What to do ?

Addendum 19-06-2021: The issue concerns me because I often need this app for local transport, but so it is unusable, which also means a loss financially.
In Google stockROM Android 10, there were no problems with the app.
As reported earlier, this app (VRN eTarif version 1.4.0) is listed in the /e/ Application Checker as working for /e/.
Now, with some effort, I got this older version and installed it, AND: the same problem as described above, the location is not recognized. In microG settings it is not registered under “Cloud Messaging”, but maybe that is because it does not send push messages.
On the “https://github.com/microg/GmsCore/wiki/Problem-Apps” page I found a note that apps using the MapsV2 API are problem apps. It seems to me that this VRNeTarif app could be one of them.
But I’m a musician and Germanist and not a programmer, maybe I’m writing nonsense now ?
@aibd and @Ingo_FP_Angel : You helped me before with advice, what do you think ?