Requiring full backup after changing from ext4 to btrfs

I’m running Restic on my synology NAS and just getting familiar with how all this works.
I’m having some issues with my backup and wondering if someone can point me in the right direction.
Initially, I ran a backup of my synology volume to an external hard drive. At that point, the synology was on ext4. After reading about the benefits of BTRFS, I decided to rebuild the synology using BTRFS. After the filesystem was rebuilt, I restored the restic backup from the external drive back to the synology.
Following that, I used rclone to move the existing Restic backup to B2 storage.
Now, the trouble I’m having is that Restic seems to think all files have changed when I try to backup the synology directly to b2. It’s using the existing parent snapshot.
Is this happening because I changed filesystems? If so, is there any way around this without backing up everything to b2 again using Restic?
It looks like it is saying that there are thousands of new files and dirs, but not a lot of actual space taken. Is this normal? I hope this makes some sense.

It is probably just scanning the files again to determine what contents (if any) has changed since the last backup.

Yes, that makes sense. You have completely different inodes etc now, for the same files.

Unless I’m missing something, restic is just scanning the files, it will not upload already uploaded blocks of data that has not changed. So it should be fine to just let it run.

Does all of this make sense? I presume you are not seeing restic actually uploading all of your files’s data anew, but what you’re seeing is that it is reading all the files without actually uploading much data (of course it will upload some metadata etc).