Numbers suddenly missing during the refresh

I noticed recently a strange behavior in the PBI Service.

I have a scheduled refresh every 30 min and usually only after the refresh is complete you can see all the numbers updated in the report and during the refresh all the numbers stay consistent with the previous update.

Since couple of weeks you can see that during the refresh one of the measures go blank and only appears again when the refresh is complete:

Before the refresh:

During the refresh (even after reseting everything to default):

After the refresh (back to normal):

I am sure that data source for forecast measure is not changed during the refresh but even then the numbers should not disappear while numbers are still refreshed?

Did anyone else notice this or have any idea on why this would happen?