I get it, as I was very confused at first too, as I understood that you had to:

1. first remove the leftmost character
2. then remove every letters "a" that are followed by the letter "b"

I finally understood that the description was confusing (to me) in its wording.

May I suggest this modification ?:

- start by removing all letters 'a', then all letters 'b', then all letters 'c', etc...

- always start with the leftmost character.

It might just be me, but for me first means before anything else (even what I just said before), and the followed by without a verb could mean both that is followed by and then.
But again, that might just be me, as I'm not an English speaker.

pit here means like a trap, or an unexpected condition

can you please describe "pit".

a b c d e f g ....

could be that u used int() in the process ? Because then it does not give you the exact result in the end if you used it several times in your code

shut up mommy

In general, I'd agree with you that it's not terribly difficult, but there is a pit that many fall into.

first remove all letter 'a', followed by letter 'b', then 'c', etc...

The letters are removed alphabetically and starting from the left.

There is no test for length of solution. So long solutions are ok.

Na, "bad algorithm", rather. ;)

The tests are "heavy" for your approach, with big intervals. That's what is causing the time out. You need to find a better approach. ;)

Some tips that could help at one point or another, maybe: https://github.com/codewars/codewars.com/wiki/Troubleshooting-your-solution

cheers