Hi @TOMillr
I don’t think there’s detailed logging specifically for FTP (unfortunately same might generally hold), however there is detailed generic logging available about things like Get and Put operations and their transfer rates.
log-level Information is enough to see file action. You can also use WebUI About -> Show log -> Live where you can choose level as you like. To see the transfer rates for individual files (not aggregate) use Profiling.
You can also look for similar problem with FTP and/or FRITZ!Box. There’s a long discussion with both here.
Debugging failures at protocol level may need expert + netstat or packet capture. Note you might have this.