Well if this is the case, you should pick one or the other. Either have complete Java placement or complete Bedrock placement.. It's current weird inbetween is causing a lot of issues with speedbuilding. Even trying to use complete java placement makes me glitch inside of blocks and slows me down.. and blocks end up disappearing no matter what playstyle you do, while building and after voting..
I feel like this is the case because of some anti-cheat that tries to make sure you aren't hacking or something, because I don't know why blocks disappear otherwise. I'm on controller, so if it thinks I'm cheating and removes blocks, OR can't register them fast enough, than a kbm player is going to have a rough time.
I don't know if this is impossible to do or how you can fix it, but I'm just here to say what you are trying to go for with the Java thing is very buggy on bedrock and breaks consistently. I'd say have Java placement on Java and Bedrock placement on Bedrock but once again, I'm not the one who codes these things, I have no idea how hard it is or if you could even do it.