Filters are not returning the complete dataset

I have a filter that was working fine before the 51 upgrade. Post upgrade it seems the filter only returns a limited set of the data mapped to the filter. I have tried both dropdown and search options and used a questions and a model to drive the filter. In all cases, the filter does not fully populate. In this case I have about 65k items that should be available to search in the filter.

are the 65K items unique?