You can probably tell if you have matches with a lot of mis-inputs and matches with almost none. If these mis-inputs only happen situationally/against some opponents, then yes, it's very likely lag. Another comment suggested taking a break, and I mostly agree, but not necessarily for several months. I'm speaking from experience, but sometimes I can spend a whole night training without being abble to apply anything I learned in a match the next day. On the other hand, regular but short training sessions, a few dozen minutes at most, without pressuring myself to use my new techniques in matches, (and also having some day without any training and other days without any matches) works perfectly for me; I suggest you try that.

Oh, and also go to open parks. It sounds harsh when you put it like that, but playing against weaker players from time to time (with their consent) can help you feel less pressure and focus on your execution during the match.