When I first changed the Kona to tubeless, I used a sealant that, whilst great at blocking larger holes, was also great at clogging valves. I've since swapped to Stans Sealant, which has proved much better. The front valve has been giving me lots of agro still, so I've purchased two new Muc Off tubeless valves that I fitted today. As usual with Muc-Off products, these are really nicely made, with an allen key recess in the base to help tighten/loosen the valve, as well as an integrated valve core removal tool in the valve cap. Whilst I was there, I also topped up the sealant which was looking a bit low.
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As well as new valves, I also treated the bike to a new chain, the old one has been there a fair while now and showing around 0.75 of wear.
I have these valves & stans too, and periodically have to change the cores. I just bought a supply from amazon and carry a couple with me. Typically I'll go to pump up/check pressures before a ride and notice the core not perfectly aligned, so just change it out. Think its just a tubeless 'feature'