Offline raster tiles does not use correct zoom level

[halset]

Platform: iOS
Mapbox SDK version: master as of f19c36a

Steps to trigger behavior

1. Load raster tiles for offline use. Extra zoom levels for tiles intersecting certain interesting areas.
2. Go offline.
3. Zoom in on one of those interesting areas with extra zoom levels.

Expected behavior

The best tiles available at any place are shown.

Actual behavior

When zooming in, first the best tiles are shown. Then the map gets more and more blury as the view shifts to showing less and less detailed tiles.

In the console, lots of messages like this are shown:

[ERROR] {}[Style]: Failed to load tile 10/527/295=>10 for source 

(The above gif show wifi and cell coverage dots, but those are turned on by QuickTime. This is really offline mode.)

[halset]

This is not related to offline packs. I do not use offline packs. The tiles got into the database without using offline packs.

[halset]

Looks like I have a similar, but less visible problem with vector tiles.

[halset]

This might be a duplicate of #9493, but that one is closed as a dup of som offline pack case. I do not use offline packs.

[jfirebaugh]

My guess is it's caused by #7741. cc @tmpsantos

[halset]

I bisected this to 9a9408e. cc @kkaefer.

[jfirebaugh]

Great, thanks for bisecting. That means this is a duplicate of #8678 and will be fixed by #9415 / #9468.

[halset]

Tried now. The current state of #9468 does not fix this problem. Hopefully it will in the future.

[jfirebaugh]

Ok, reopening so we can investigate.

[halset]

In this case, it looks like my offline tiles are expired. So it first draw the old one, then tries to fetch a fresh tile and then when the network is down the download failes and it jumps to z-1. It should probably use the tile in the database in this case even when it has expired. Does this make sense?

[halset]

I worked around this issue by making sure that the offline tiles that I insert into the database has a expire value in the future. That seem to prevent mapbox from attempting to refetch the expired tiles in offline mode and then failing resulting in jumping to z-1.