Grows on peaty thin soil on tundra together with Salix arctica, Cerastium arctica, Carex fuliginosa subsp. misandra and Bistorta vivipara.
It looks like something in the Cortinarius genus, which has many difficult-to-identify species. The third photo seems to show remnants of a cortina around the cap edges.
Agreed Vitog, it looks very Cort. I'm so very glad to hear you will be vouchering a specimen sepo! Your habitat notes on proximate shrubs/plants will be valuable. Also, if it was possible to collect the stem base for any of these, those will make the best ones to send in.