Thanks all for the inputs and tips!
We've got 6-12 loggers running in a test setup now to identify the error.
In the below link we have the FTP log in a google sheet:
https://docs.google.com/spreadsheets/d/1KWBoUGJMa7sF1b8WsRUJASdiT3deM59KnjbQAXG6uKo/edit?usp=sharingIt's really strange:
Our loggers generate ~30 MB files every 2 hours and send them to the FTP server.
For most of our transfers, we don't get any issues in our setup and files are transferred within 5-15 seconds, no problem.
For 2 transfers, we do encounter a timeout that appears after 10 minutes. After this, the logger would usually not resume transfers later on, but we use a "recovery" mechanism in which we turn off the power for the FlashAir (via the logger itself) for a short period to simulate/force a reboot of the card.
After this, the "timed out" file is transferred upon the next file split as per our recovery specification (cf. the colored lines).
However, the third time an issue occurs there is no resuming.
Apparently our "recovery" mechanism fails, maybe because the card does not fully turn off - or something else plays in.
It's a super long shot and I don't expect anyone to have suggestions here - just wanted to share for update purposes.
Should any of you have ideas/suggestions for how to test/identify the issue, it'd be helpful.
Note that the data logger is not easily able to get any info from the FlashAir as Toshiba probably never intended fully for this kind of use case.
Martin