Hi Smbls,
Welcome to our forum.
Did this issue occur when you dial in an internal conference?
Did this issue occur when you dial in a federation meeting?
To this intermittent issue, we suggest you renew SFB certificate wizard on FE, Mediation server and Edge as the following snapshot:
When it failed, please check if there are any errors in application log on mediation server and post them for our troubleshooting.
If there are any questions or issues, please be free to let me know.
Best Regards,
Jim Xu
TechNet Community Support
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