It could be the valve, but it isn't uncommon for tires to take a few days to fully hold air tubeless. I set up some Ground Controls on my DTSWISS BR710 and the front one didn't hold air the first day or two. After a ride it worked fine. By the way, riding the bike is the best way I've found to ensure the sealant is splashed around.

Loon for sealant around the valve, bead or the rim cutouts. If you see any it could be an indication the tape is the problem.