This may be due to changes to tags mid-month and how CloudHealth treats them following the change.
When tags are changed during the month, the platform honors the latest change to the tag of the month.
For example, if Tag 1 was changed from A to B on February 7th - the tag will reflect value as B for the entirety of February (as opposed to splitting the tag values for a given asset based on the date). It is expected that tag changes mid-month may not line up in the Azure portal for a given month due to how CloudHealth treats this scenario.