This is in part due to the new way in which the geomodel is produced. There are no Research Grade observations of this species in the UK, and only two in Europe (which I have just now knocked back to genus) but the geomodel predicts that the species could occur across Europe. This is a known problem with the geomodels and affects other species, too. See other discussions about the geomodel on the Forum (e.g.). How the geomodel is calculated is still being refined by @alex and others on the iNaturalist team.
The list you are looking at is limited by location, but there are still errors because of the geomodel issue mentioned above. You can see the Ichneumonidae recorded with Research Grade iNaturalist observations in the UK here: https://www.inaturalist.org/observations?place_id=6857&quality_grade=research&taxon_id=47199&verifiable=any&view=species
There will be species missing, because nobody has yet observed them on the platform and had them confirmed. There are also likely to be some errors, because, as you know, some of these species are difficult or impossible to identify from photos. If you see any errors, and have expertise to correct them, please do! That’s how the platform works. iNaturalist is very effective for taxonomic groups where records are actively reviewed and corrected by taxon specialists, and not so reliable for groups lacking active, expert identifiers.
Anyone with expertise in a taxon can make an important contribution to improving and maintaining data quality on the site. In a group such as Ichneumonidae, where there are many errors in identification, I’d suggest to prioritise correcting Research Grade observations, as there will be fewer errors to correct and you’ll have a direct effect on the data exported to GBIF.
You could, for example, scan through the 136 species with Research Grade observations in the UK (from the link above), starting from the bottom (species with a single record) and check for errors there. If you find any, please feel free to suggest a different ID on the observation and to ask how it was identified.