Right. [aeiou] can only ever capture one character at a time, so it's not able to deal with consecutive vowels any more efficiently than any other case.

Is it because it creates less matches?

Unfortunately most of the tests are compile-time and therefore quite slow, and the codewars servers have inconsistent performance regarding that. However, writing a concise proof will also speed it up considerably.

Or: try to submit few times every day. Maybe CW server is chocking when you're doing this, which does not happen everyday.

There're performance tests. You'll need a faster proof.