that makes sense, actually in the first run, when target is empty, rsync will just send everything without comparing and/or waiting to traverse the whole tree. If restic needs to read every file and hash it, then it would explain why it takes its time pacing through several dozen TB of files.
Before I opened this thread I saw: Randomly Needs to Rescan All Data - #35 by fd0 Show I supply --ignore-ctime to avoid the random rescan?