looking at the first 4, the 1st, 2nd, and 4th having missing dates, and the 4th has a missing photo. all of these were created many years ago.
i looked at a copy of the AWS Open Dataset that I have from April 2021, and these observations already had missing dates at that time. so if the dates were removed, then they were removed before then.
these observations were created in the Android app. so if there was a problem, i suspect the problem was in the Android app. where the photos exist, the metadata in the photos does have seemingly valid dates recorded. so i don’t know why the observations wouldn’t have been recorded with valid dates originally. i guess the good news here is that the observation dates could be restored using the dates in the photo metadata.
there’s an old bug report that may be related to the observations missing dates: https://forum.inaturalist.org/t/large-number-of-app-users-with-date-observed-missing/11498.