Nextcloud Box Ubunto Appliance Crashing on large data transfer


I have Nextcloud Ubuntu Appliance on my RPi3 Nextcloud Box which has an external hard disk, and the 3.1.2 Client on Manjaro Arch Linux

All is working perfectly, except for when I change a lot of files on my Laptop (e.g. 30GB) the client starts syncing OK, but then the RPi crashes every hour or so.

At least I think it is crashing as the route to host is lost for SSH from Laptop.

What are the relevant logs that I should look at to see what is happening please?
(well so that I can post on here to ask someone how to work it out :grinning: )


PS I have used the below before after physically connecting the box hard disk to the laptop and copy the files over (with cp -pr ) but I am now trying to get it to work via the client for large data exchanges
sudo nextcloud.occ files:scan --path="<Nextcloud user_id>/files/<name given to disk in Nextcloud>/<Directory of interest on external disk>"

OK, now I have a bigger problem - it seemed to be working better so I left it overnight but this morning I have the following error:

500 internal server error to PUT ...