It is likely that the link for the password has simply expired, meaning it will no longer work. There could be two possible explanations.
You may want to review the timeouts that you have established for your Forgot Password Workflows Tenants > Your Tenant > Advanced > Change password to ensure that you are satisfied with their duration.
The user sent themselves two password reset emails in a row. The first password reset link sent would be invalidated (expired) when the second request for a password reset is submitted by the user. If the user then clicked on the first password reset link (in their inbox), then they would have seen an expired message.