Redirection urls

Might be a silly question, but one of our clients does most of their own changes to the website we once build for them, so they also installed your plugin to use. Seems to be working fine.

But they are seeing some ‘edited’ urls after redirection. they have a couple of forms each with its own thank you page. but the pages now contain some extra random numbers/letters in the url. so instead of /thank-you it becomes /thank-you-34252VS

I assume it is some kind of tracking. manually changing the numbers to something random does nothing (404).

But I don’t know where it is coming from. So I was wondering if this has something to do with your plugin, or if I should be looking elsewhere.