Have you tried using another browser?
From a quick search and AI explanation, it seems that, with the HTML language used to create websites, the creators can implement a pattern check, typically for email addresses or phone numbers, so that the browser on your computer will check that the input matches a certain format like the presence of the @ or a domain for an email.
For a password, this is unusual because requirements such as symbols or capital letters are usually checked by the server and not by your browser in your PC.
Different browsers can implement the pattern attribute differently, so that's why you could try that. You could also clear the cache and cookies of your browser.