If you can get the troubleshooting log from the device, that might provide more info. (In Field Maps, click on the profile icon, scroll down to "Troubleshooting", then click on "View Logs". If logging is off, turn it on, then try to create an offline area again. You can also clear your logs, then try a new offline area, and this will keep the size of the logs down and things cleaner if you end up sharing the whole log.)
That said, these logs can be quite large and might reveal information you may not want to expose by sharing all of it (not to mention the device might struggle a little depending on which app you try to share it with.) I recommend using the search box to look for "error" and then separately try "fail" as a pretty good start to see what might be going wrong. These client logs only tell half the story, so the rest would be a server log for Enterprise or in logs in AGOL (maybe), but then you are getting closer to needing a ticket if you do not have proper access.
Esri support recommended we keep removing half the layers until we resolved a similar problem. I suggest saving the map as a new map each time, or using ArcGIS Assistant and saving the JSON if you are familiar with that, just so you can get back to where you started easier. Layer-by-layer works, as well, but you might save time by removing 50% of the layers/tables each time if you have a lot of layers and/or tables. (If you had 20 layers, and you removed 10 and the map works offline or not, now you quickly only have to troubleshoot which layer out of the 10. Whereas troubleshooting layer-by-layer, you might not find that problematic layer until your 10th try in an unlucky scenario. Takes a bit of the luck out of the equation, but I see value in both types of troubleshooting.
My apologies if some of the above is obvious, but I never want to assume that someone knows what I am talking about when troubleshooting a problem.
I hope this helps.
Mitchell Grafstein, Horticultural Inspector 1, NYS Dept. of Agriculture and Markets
