For some reason, I tried to snap a subdir of a dir already snapshotted recently. Files are unchanged between the 2 snaps. Kopia started to upload data. I canceled the snap, but it looked like it was uploading everything from scratch. In the logs, I can read messages like: “could not find cache entry for file1”. Mounting the snap of the dir, I can check that file1 is here and is byte for byte identical to the original file.
I could not reproduce that using randomly generated test files in a subdirectory.
Are you actually seeing network uploads or just the process taking a long time? I suspect the latter and Kopia is just hashing the files again to determine they don’t need to be uploaded.
Because of compression used this will sometimes cause a reupload, though (but this particular case will be fixed in v0.9 thanks to new index format)