i have been running tubeless tyres for a couple of years with no problems.
however, last week my rear tyre (maxxis minion d/h 2.5 on a deemax rim) kept losing air but only when i rode it. I could pump the tyre up at night and it would be fine the next morning but if i pumped it up and rode it then it lost air very quickly. In the end i put an in ner tube in and it was fine. there didn't appear to be any holes in the tyre.
There appeared to be sealant leakage around the rim where the tyre sits but i have assumed that this is a consequence of riding with a flat tyre rather than the cause?
Any suggestions
I know it sounds daft, but has the removable core in the valve come slighty unscrewed?
i wondered that also but i had to take it out to put the inner tube in so i guess its worth a try to refit etc
Is the bead damaged?
just accept tubeless doesn't hold up for DH, especially for rear wheels.