Currently, uploading a multi-commit review request diffs fails with

"API Error 207: Repository File Not Found" when different files are

changed in different patches.
See the report here:

https://groups.google.com/g/reviewboard/c/FG5TNTNC_fU
It tries to request a raw file from a server repository using the

revision ID of the previous uploaded commit.  Sure there's no such

revision on the server as those patches aren't pushed yet to the

upstream repository in a pre-commit review case.
For a proper file request in this case it should use "base_commit_id".

Reproduced the original problem in a new database, and verified that

this fixes the issue.