The following was posted on Bibliocommons partner portal:
Libraries who have upgraded to Polaris 7.2 will no longer be seeing updates for bibliographic, item, and authority metadata reflected in their BiblioCore catalogs on an hourly schedule.
At this time, the cause has been identified as an issue with the Polaris API Synch_ methods.
In Polaris 7.2, these methods do not appear to be correctly interpreting UTC offsets provided in timestamps. This behaviour has not been identified in any previous version of Polaris, including versions 7.0 and 7.1. These two versions are responding as expected.
Because of this, we strongly recommend that libraries do not upgrade to Polaris 7.2 or 7.3 at this time.
My theory was correct, here is what we got back from support:
While this had not been a problem in Polaris 7.1 or below, the API was updated in Polaris 7.2 from .NET Core 3.1 to .NET 6. Amongst other changes included with .NET 6, Microsoft made an update to how time offsets would be used in datetime calculation. As a result of this change, the datetime that is passed into the API appears to advance the time by the value set in the offset rather than subtracting it, meaning that the example above now passes a time of 3:00pm into Polaris rather than the 7:00am that BiblioCommons is expecting. Because of this, Polaris sees their call as requesting a synch of items modified at a future time, so there is nothing for Polaris to pass back.
Bibliocommons are the ones that need to make the change:
We provided this information to the BiblioCommons team and they are currently working to update how they are passing the date in the Synch calls in order to allow them to be successful.