Hello @Kevin_Li and welcome to the forum!
Was this one at 5/25/2019 1:35:44 PM one of them? This looks unsuccessful, but maybe others were OK.
New warnings/errors occurring after updating to 2.0.4.5 has the reference, but they were part of the debug effort for an old problem that was fixed once, has come back, and hasn’t yet been debugged/fixed again…
The cause is better understood, and is often backing up a file that’s being actively modified during backup. Specifically, it’s often the journal file for the Duplicati local database for the backup that’s currently running. The summary line doesn’t give enough detail, but you can look at server log (About → Show log → Live) at Error level (Warning would also work, if you want details on the Warnings as well) to see further details.
Database field Local database path shows your local database, and when use it sometimes generates a temporary file which is the same except with a -journal suffix so the name ends in .sqlite-journal.
Warning: sqlite-journal errors 1400 gives two solutions, if this is what happened. One is to exclude the file, and another is to use –snapshot-policy (if you have Administrator privileges) to get a stable view of the file.
Being a little more specific about backup folders can also help. It looks from the Warnings like you do C:\ which is probably going to run into some other locked file problems (so benefit from snapshot) eventually.