Hi @mikel. Apologies for the confusion—I can totally understand how the new stuff wasn't very discoverable!
I think that leaves just the first issue, with your tiles disappearing. I tried the osm-kabernet.mbtiles file you uploaded, and so far I haven't been able to replicate the issue. I'd love to figure this out; do you happen to have a sequence of steps that will reliably trigger the problem for you?
In my experience, the tiles sometimes seem elusive because they only appear at the zoom levels they are declared for. So if I don't already know where they are and I don't know what zoom level they're at, it can be hard to find them and zoom to a point where they appear. In this case, your file doesn't have a minzoom or maxzoom declared in its metadata, so the tiles are only visible at their individual zoom levels. The file only has tiles at levels 4 and up, which means that if you are at zoom level 2 or 3 they don't appear. (If minzoom were, say, 2, then the level-4 tiles would continue to be visible even as you zoomed out to level 2.)
So when I loaded the file at first, it seemed like I couldn't get the tiles to appear. But now that I know what part of the world to zoom to (I zoom so that Ethiopia fills the screen), they appear for me every time, online or offline. I don't know if this might be what's making it seem like the tiles aren't showing for you—were you at the same zoom level when the tiles weren't coming up?
I also noticed that the set of visible tiles covers a different area at each zoom level, so as I zoom in, the square of tiles jumps around. But I think that's how it actually is in the file, so it's the expected behaviour even if it does look a bit weird. Is that what you expect as well?
Thanks for helping us investigate!