This has now popped up again with a different site. Users report it started after we enabled on demand call recording for all the extensions. It only happens on the D series phones. It’s a small site with 2 D series phones and 3 sangoma Dect cordless.
I have another site that had older D40 phones. They were on FreePBX Distro 14. Their hardware died so I moved them to a new cloud server with FreePBX 16.
The issue started immediately with their phones. Since the phones were so old I convinced them to upgrade to new ClearlyIP phones. Issue gone. So this is definitely an issue with Sangoma D Series phones or EPM.