I think this is a pretty common problem with a lot of records that are entered by importing geo-tagged photos, whether they were taken with a smartphone or camera. I’m not sure whether this is because the device did not record accuracy or if something is happening when iNaturalist reads the photo’s exif data.
In fact, doing a query reveals that there are 6.5 million verifiable records in iNaturalist (22.5 % of ALL VERIFIABLE) with coordinates but without accuracy. Most of these records are very hard to use for any conservation purpose because it’s impossible to have any idea how accurate the location is.
Here’s the query:
https://inaturalist.org/observations?acc=false&place_id=any&subview=table