Thanks for reporting this. Credentials provided by a Dynamic Folder are dynamic objects and therefore cannot be changed. We’ll adjust Royal TS so that, in this case, the Auto Fill configuration is saved with the web page connection instead. This will ensure that the configuration is retained when the document is saved.
As a workaround, you can “disconnect” your credential in the web page connection to force Royal TS to store the Auto Fill configuration in the connection object and then assign the credential again.
The next release will have this fixed. Sorry for the inconvenience.