A grid of white seams across the map almost always means the device's display scale changed while DMD2 was in the background — the Android setting usually called Display size or Screen zoom. The map engine caches rendered tiles against the scale it started with, so when it comes back to a different one the tiles and the view no longer line up.

DMD2 now repairs this itself. On returning to the app it notices the change and reloads, showing "Display scale changed — reloading…". That reload is deliberate, not a crash.

You will see a similar notice, "Map scale changed — reloading map…", after you change Map Settings → Map Scale. Same reason: reloading cleanly is the only way to avoid seams or a white map.

If stripes are still there after a reload, restart DMD2. If they survive that, the cause is the phone or tablet's own display-size setting rather than anything wrong with your map files — set it and leave it, and the map will stay clean.