I am using restic / rclone to a jottacloud backend. Very few errors; they get corrected by rclone/restic, except for one error as described in Http2 stream closed / connection reset / context canceled - #10 by MichaelEischer - Getting Help - restic forum
I am waiting for a fix in the go library..
Currently about 3.6TB on jottacloud. As far as uploadspeed, I get around 10MB/sec (on a 60MB/s connection), but I have the feeling that the bottleneck is restic running on an arm processor.
I don't have big data as far as download-speed. At every single backup (every night), my script tries to download and verify one single random file and with that there are no issues.