I had this error all weekend and needed to revert to the old app. I tried flushing the project cache and re-fetching project tiles, also changing the tile resolution - all of those succeeded but the main page still showed the error.
The issue is now happening persistently for me and makes the app unusable.
The error message in full is:
Web page not available
The web page at file:///data/user/0/com.trapnz2019/files/2.5.6/leaflet.html could not be loaded because:
net::ERR_ACCESS_DENIED
I’m on v2.5.6 updated 1/10/19, which apparently has a fix for ERR_ACCESS_DENIED loading map on android. The problem has only been happening for me since this new version, having used it without problem for a few weeks beforehand.