I was running into things getting stuck both creating the offline areas as well as downloading them.
As you know, you can't have a web map WITHOUT a basemap. Even if you select in Field Maps Offline tab that you are going to use an installed tile package for the basemap, it will still try to tile the basemap of the web map itself at the level of detail selected when you create the offline areas.
Default of "Neighborhood" can still be quite huge, and limits the size of the offline area you can sketch.
So, I created a simple vector tile package with just the City Limits polyline layer, and nothing else and set this as the basemap in the web map itself. Now, when I generate my offline areas, since the basemap is tiny (and not a huge tiled basemap that will be stuffed into the offline area when created), I can select the entire city (or whatever portion of it I want) as the offline area (even at LOD=Room), and it packages it just fine.
Then, I just use the "actual" basemap that is sideloaded on the device itself and all is good.
Since I switched to this method (having a tiny vector as the web map basemap), have not had issues creating/downloading the offline areas.
Hope this helps,
R_