Yes, I still think it is something to do with the culture settings. We have a bug logged for this and it should be fixed for our next release.
In the meantime, I have another workaround for you. Again, it is not ideal, but hopefully it will allow you to sync. You can turn off syncing for just the Priority field on bugs. To do this you will need to modify your sync mappings by following the steps laid out in the documentation: Editing Synchronization Mappings. (Please save a local backup of these settings before you modify them.)
You will need to find a line in the mappings in the Bugs section that looks like the following, and remove it.
<FieldMapping TeamPulseFieldName="Priority" TeamPulseFieldType="single" DestinationFieldName="Microsoft.VSTS.Common.Priority" DestinationFieldDisplayName="Priority" DestinationFieldType="integer" />
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