I just did a one-directional test - syncthing is running as syncthing user with elevated privileges. I added a directory called “on-hold” on server A - set the octal for 2775 - group is “project” - owner is “ejmccull” > it synced on server b with octal 775 - group “project” - owner is “ejmccull”.
Group and Owner are transferring correctly - Octal is not.
Send Ownership & Send extended attributes are selected on Server A
Sync Ownership & Sync Extended Attributes are selected on Server B
Not syncing the first octal digit is working as designed. If you have a need for that, describe your use case and make it a feature request. But these bits don’t translate easily to other operating systems, so the design needs to care for that aspect.