this elaborates a bit on what @fffffffff said above: https://forum.inaturalist.org/t/observations-dont-upload-into-a-project/12315/2.
i checked a few of your examples, and as far as i can tell, the system is working as designed. (there is no bug here.)
for example, you noted this as an observation that is missing from your project:
although the observation detail page does not list your project in the project list (because the user is not a member of your project), if you search for observations by that user in your project (https://www.inaturalist.org/observations?place_id=any&project_id=washington-native-bee-society&user_id=mariol2), you do find the observation. (in other words, it’s not actually missing from your project.)
