Thanks for reporting. I just deployed a fix for this and hopefully the counts are accurate again. The bug was in how the data was being cached when multiple place_ids were provided.
FYI a better way to search on multiple values of a parameter is to provide them all in a comma-delimited list rather than repeating the parameter multiple times, e.g. https://api.inaturalist.org/v1/observations/species_counts?verifiable=true&place_id=7613,10301