I have an Office 365 driver matching rule that works fine on a test
tenant, but not on a production tenant. The only difference between the
two is the number of records. The test tenant has about 25, whereas
production is about 2000.

The matching rule queries for UserPrincipalName. With the test tenant,
the shim finds the match. With the production tenant, the query is
returned OK, but no match is found.

My suspicion is the problem may be due to the size of the data set. I am
curious if anyone else is having this issue -- before I open an incident
or report a bug.