I sure know about this - at the moment I'm preparing a modRana bugfix release (should fix the map layer switching bug) and after that I plan to return my attention to debugging the 1080p-black-screen issue, primarily in the form of adding more debugging messages, so I can track the issue down. In any case I suggest watching (or even subscribing to) this issue on GitHub:
https://github.com/M4rtinK/modrana/issues/186

That's at the moment probably the best place where to watch for progress in this matter, even though I'll probably also post updates to this thread.

And sorry for this taking so long - the issue seems rather hard to crack so far. My current theory is that it's either some pretty particular race condition (happens at 1080p only, not above or below & only on Sailfish OS) or even possibly some platform adaptation glitch modRana manages to hit on the ex-Android 1080p devices running Sailfish OS.

Actually the two devices seem almost identical in screen (1080x1920), SoC (Snapdragon 801) and GPU (Adreno 330), so I guess a similar hardware adaptation/drivers are used for both ?

It would hardly be the first Sailfish OS specific weirdness I've hit during modRana development:
[bug] MouseEvent x and y properties are floats
[bug] Some QtQuick Canvas drawing coordinates cause application-wide deadlock

BTW, so far the issue seems to happen on Fairphone 2 and OnePlusX - could someone with Sailfish OS running on a phone with 1080p screen verify if current modRana runs fine or if it has similar issues ? That could help narrow the search for a cause down.

If it also happens, it would be more likely some modRana side algorithm is at fault. If modRana works fine then it would be likely specific hardware adaptation glitch is at fault.