Had something very similar on my 819 rim – so tubeless and no spoke as fully sealed rim.
First off it refused to hold air, with air leaking out around the valve, so i thought it was the valve. Ended up sealing the valve in, but air just came out from round the spokes.
So, popped a tube in and all was OK for a while, then a puncture … then another, so I blamed the newly surfaced towpaths.
Tyre changed to a proper commuting one, so nice and tough. Still got a puncture every other day. Eventually realised the punctures were all on the inside of the tubes, and then I found what I thought was a big scratch along the rim (running along the bed, not across it). So I filed it, thinking it was burrs rubbing through the tubes.
And another puncture … so I took the rim off (OK, I cut all the spokes with wirecutters, so “took” might not be accurate) and sent the hub off the JRA to be built up again. Once the rim was off what looked like a scratch was a big crack that was expanding – as I say, along the rim bed around the rim rather than across it. So the crack was opening under load and “biting” the tube.
First rim I’ve every had fail. Worth checking yours?