Max offline buffering?
There should be no limit.
Do you know if the fixes are stored in a way that they might be lost if the phone crashes or is shutdown due to overheating? (Should be a clean shutdown I'd think).
Anything is possible, but unlikely. They are persisted on disk.
Persisted on the android storage? What's the normal purge cycle?
The last fix was when I left service, then there's a 3-4 day gap, and it starts again 4-5 days into the trip. No fixes in between, and I didn't change the network/location settings during the trip.
Yes, Android storage. There's no purge cycle.
I did a test over the weekend, and had similar experience. To test I blocked Traccar Client from network access for a few days. When I gave it network again although it was still logging GPS fixes, it didn't attempt to upload them. It wasn't until I clicked "send location" that it started uploading the queue (I had to click send location last time too, despite having had network for hours after we got back into service). After everything uploaded I checked and most of the weekend was missing from the server, only the most recent fixes were there.
To replicate I'd suggest disabling network for a few days, then re-enable. For me, no upload happened until I hit send location. Then, only the most recent fixes showed on the server.
What is the limit to offline buffering? I just returned from a wilderness trip and was hoping to have a track recorded via Traccar.
Once everything uploaded I found that only the most recent section of the trip was uploaded, so I'm lead to believe there is a limitation to offline buffering. I checked storage and Traccar was only using a few hundred MB, so it wasn't impractical to cache more.
If there is no limit, perhaps the cache was cleared when the phone restarted during the trip? Either way, would it be possible to extend the limit?