There seems to be quite a ridge around the valve area
sounds like somethings not seated right.
I did get a maxxis dhr 2.35 dual ply on a 5.1 rim using a bmx tube, took a compressor to get inflated tho, did one big ride it was fine. Left bike in cupboard went back 2 weeks later it was flat with bead unseated. Reinflated and it just deflated again within 30 mins.
Did get a rimstrip for 5.1 but couldn’t get a dual ply or UST tyre on (and I shred single ply tyres) so rim strip for sale. Dunno if it was the battered old rim or not enough sealant. I rebuilt the wheel with a flow, used yellow rimstrip, valve, 2 turns of electrical tape and dual ply tyre. Again I needed a compressor but works fine. Same problem tho left it for a few weeks* and it’s flat but bead hasn’t unseated so more sealant, inflate, shake and it should be fine.
*big bouncy bike, it doesn’t get used very often