Hi Peter,
Have you tried checking your entity access? Try giving read for this attribute to all module roles. I've had a similar issues with an attribute value being set in a microflow, but when I commited the object, all other attribute values saved, except for two. The issue was fixed by giving read access to all module roles (previously the access rights was set to none).
reference to this question:
Hi Peter,
This is a bug, either in the platform itself or your database got corrupted somehow.
The autonumber documentation is quite clear. There shouldn't be any exceptions or special cases causing such a behaviour. So, file a support ticket for this.
regards, Fabian