Hi there, thanks for the thorough reply.
No I don't have the experimental beta.
Yes I use Steam Cloud, and to go one further on that, I know the directory it's downloading to and I can see it downloading the folders, but they're empty.
I had seen that creating a new profile might restore things, but unfortunately this doesn't appear to be the case with me, as it will only show me the new profile.
However, I had found a semi "fix", though it's not ideal. Out of paranoia for this exact thing happening, I regularly back up my games files for ETS2 elsewhere, and I was able to put them back in the right places and that recognised it and my profiles were booted back up. The unfortunate part is that I've lost a month's play time, about 7 trucks, 8 drivers and a garage in Stockholm, as there was an update between backing up and then which caused the files in .bak to shift to another location that wasn't backed up, but it's nothing I can't get again.