There for sure is an issue. I'm currently crossplaying. 1 player, who made the world on a Switch Lite, one on a phone and me on my laptop. Connected to 1 world on the same wifi (no realm or server). They are having no issue, but my hunger goes down at an insane rate.
I can fill my entire hunger bar and less than a minute of running and almost at 0 hunger bars. Basically unplayable.
It's really annoying. And it 100% is because of migrating your account.
Using 2 different installations of Minecraft, 1 logged in with my migrated account and the other with the account that is still a Mojang account. The microsoft account takes ~20 seconds to load, the Mojang account is pretty much instant (does not see a loading animation at all).
I guess it has to do with connecting to the Microsoft services? Whatever the reason may be, it's pretty awful that this is the way it is.. considering it's always been great. Why force something that wasn't necessary if it's just gonna get worse for the players.