Help with Calculated field - Calculating the number of related records in AGE 10.9(Azure)

[FionaRenton1]

I have a related table in ArcGIS Enterprise using the classic map viewer. (Relates don't work for field maps in the new map viewer on AGE 10.9 yet unless I am mistaken).

I want to use the calculated field to be equal to the number of records in the related table (SiteVisits). This way I can set a status field for sites that need to be visited.

When clicking test this gives me an expected number, but when I click OK it just hangs and never calculates anything in the table (only 70 records). I'm hoping it is a user error that is fixable!

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return Count (FeatureSetByRelationshipName($feature,"SitesVisits"))

[FionaRenton1]

This is now logged as #BUG-000151157 Arcade expression with the function count() hangs and does not calculate an Integer field in the classic map viewer of Portal for ArcGIS 10.9.