I'm not sure if this affects only takeover mode (ts/js files) or also Vue files but I would suspect that it does affect all.

1. Create files:

file1.ts

export const x = 1;

file2.ts

import { x } from './file1';

export const y = x + 2;

2. change 1 in the first file to 'str'.
3. Switch to file 2

Expected: file2 shows an error because number and string can't be added.
Actual: file2 does not show any error until something is changed in the file.

It doesn't seem like Volar listens to the tsserver events (syntaxDiag, semanticDiag) that update diagnostics.