Pure Maps rendering issues

Pure Maps, as distributed via Flatpak, fails to render map fully on L5. Issue was triggered after updating Pure Maps Flatpak runtime to the latest available one: KDE Qt 5.15 based on 20.08. See example of the problems at https://forums.puri.sm/t/puremaps-flatpak-on-the-l5/11203/17. Rendering can be corrected by using software renderer:

LIBGL_ALWAYS_SOFTWARE=1 flatpak run io.github.rinigus.PureMaps

Issue is not observed on other platforms such as on desktop Linux, Sailfish and Ubuntu Touch. There are some rendering issues on PinePhone, but those were already reported earlier by others and are probably not related.

Unfortunately, it is probably difficult to debug as we have separate Mesa implementations in Flatpak container and OS. To my knowledge, Pure Maps has not been fully packaged for Debian-based distributions, but maybe someone in Purism has proceeded with this effort. Please fill in then as it may simplify debugging.

References: Issue is based on user reports starting from https://forums.puri.sm/t/puremaps-flatpak-on-the-l5/11203/17 ; cannot test it myself.

Filing it over here as suggested by Dorota.