Here you will find a complete list of known problems on Mac if your signature does not update.
If the signature is not updated and/or the upload is running in a vacuum, open "System Preferences" on your Mac, click on the "Security and Privacy" icon and check that in "Automation" the boxes related to Signitic are checked.
Give access to the disk
Go to the Full Disk Access tab and adding the following 3 applications : Finder, Terminal and Signitic.
If you still can't retrieve your signature, we invite you to add "signitic.app" to the white list of authorized websites on your Antivirus/Firewall.
Please refer to the documentation of your software.