Here are some links to make exploring this issue easier:
taxon page: https://www.inaturalist.org/taxa/48502-Cercis-canadensis
clicking April/flowering: https://www.inaturalist.org/observations?verifiable=true&taxon_id=48502&term_id=12&month=4&term_value_id=13
uncheck the Verifiable filter: https://www.inaturalist.org/observations?month=4&taxon_id=48502&term_id=12&term_value_id=13&verifiable=any
For me I see 823 observations when I uncheck the verifiable box. I wonder if that last missing one could be related to this bug report: https://forum.inaturalist.org/t/downvoted-annotations-are-included-in-charts-on-the-taxon-page/18151 do you see 823 observations when you log out of your iNat account?