The reason I ask is that I’ve seen a local report similar to yours where transmission stopped after a period of time.
In that case it looks like the data rate reduction appears to be happening even if ADR is set to off at the application level.
In this local case disabling the code that decreases the data rate within the runtime appeared to have solved the problem.
If data rate reduction is still happening and you are transferring more than the LORAWAN_DEFAULT_DATARATE allows, the transmission will fail.
Do you know if the app is hung, requiring the watch dog reset vs it’s still trying to transmit but the transmit fails? Perhaps turning on an led if the transmit fails, off it it succeeds. A constant on would tell you it’s always failing. That would need to be done in the lower runtime code.
I’ve not yet confirmed this but that is my next task. I’ll report back what I find.
Regards