Hosted Feature Layer issue after 10.9.1 update

[MichaelK_MTDEQ]

We updated our ArcGIS Enterprise system to 10.9.1 over the weekend and are now seeing the error below on layers published through portal pre the update. 

{
"error": {
"code": 500,
"message": "Invalid ID for region-based ZoneId, invalid format: Mountain Standard Time",
"details": []
}
}

Has anyone seen this issue and maybe knows of a fix? 

[MichaelK_MTDEQ]

Changing this in the service definition from "Mountain Standard Time" to "UTC-7" gets it working again, just not sure this is the best way to fix it. 

"dateFieldsTimeReference": {
    "timeZone": "UTC-7",
    "respectsDaylightSaving": true
   },

[MichaelK_MTDEQ]

On the portal item, going to the layer that is affected. 

If you adjust the "Time Enabled" setting at all, it will fix this issue.  

For some services, we turned it on, and then back off. After that it was working as expected.