Welcome to the forum @benhen31
Did you find a file of that name? If so, what size is it? I think this is saying it’s 0 and should be 23 GB, which I’d call way too large for reasonable performance, but you did say you you were testing 50 GB.
What size were the earlier dblock files? The default is 50 MB. Choosing sizes in Duplicati has advice. Ordinarily you should have a flow of dblock files at about the size limit, and much smaller dindex files.
WebDAV, pCloud, Duplicati is a recent case where pCloud WebDAV broke then they fixed something. Whether or not this is relevant here is unknown, but signs seem to point to upload/download issues…
would be a download issue, probably during Verifying backend files where something verified wrong.
Given the Warning above it talking about length and hash, I’d guess it’s an empty file. Can you look?
For any future tests, it might be useful to back the remote volume size down, and watch live log from some subset of the 30 GB. About → Show log → Live → Retry should give more info on any errors.