Understood. Take your time.
You can also try to leave only my plugins ON in your project to really check if it is a compatibility issue.
I do think it is, because using my Diagonal character Plugin and this Jump System Plugin, when the diagonal parameter is off, the diagonal jump is really prevented. All three work together just fine.
I could suggest you to disable the diagonal feature from visustella and try using my Diagonal Character plugin, which is free. Just install it somewhere below the visustella one.
Hakuen Studio Diagonal Characters for RPG Maker MZ by Hakuen Studio
If that still not works, then we can return to the first alternative to fix the compatibility problem. But for that I will need a sample project.