A family of Microsoft on-premises document management and storage systems.
My issue turned out to be related to us hardening our servers and requiring TLS 1.2 on our SharePoint servers. I followed the steps in https://learn.microsoft.com/en-us/sharepoint/security-for-sharepoint-server/enable-tls-and-ssl-support-in-sharepoint-2013.
Please note that step 1.4 - Install SQL Server 2008 R2 Native Client update for TLS 1.2 support is required even if you are on a newer version of SQL Server, such as SQL Server 2012 in our case.
you will see error in ULS logs: UserProfileApplication.SynchronizeMIIS: Failed to configure MIIS post database, will attempt during next rerun. Exception: System.Configuration.ConfigurationErrorsException: ERR_CONFIG_DB
helpful was: https://github.com/microsoft/tigertoolbox/blob/master/tls1.2/CheckClientUpdates.ps1 and https://www.microsoft.com/en-us/download/details.aspx?id=57606 where I had to try every file because they are not documented well, eventually one worked. No reboot is required.