Feeling like this is pretty common with a lot of people..
Try cutting down the dosage even more.. Sometimes it could be the type of Kava strain you are taking as well.
Sometimes it could just be Kava itself.
In addition to what others have said, I find things like stress level, tiredness, set/setting, and the like can trigger a feeling like that. In particular I would say that being very tired and drinking kava can really push you to that point.
I've been experiencing dyspnea for almost a year now, and kava seems to be the only thing that relieves it (to be fair, I havent sought explicit help for this issue other than getting covid tested to be sure it wasn't that, to which they gave me the full work up, chest xray and whatnot). You're not, by chance, using a low quality kava or mixing it with alcohol/kratom though, right? Those substances can definitely cause dysphoria on the "down". I've never experienced this directly because of kava consumption.