One of the situations where this problem occurs is when you’ve submitted too many attempts. To resolve Gmail forgot password not working, you must know that Gmail limits the number of attempts to protect your account from getting hacked. So if the number of attempts exceed the limit, Forgot password option stops working. The recovery option will be re-enabled on the date indicated below that recovery option. In the meantime, you can use a different recovery option.
Read all above Official Blog Post To Fix Gmail Account.