When logging in by guest users, they have to use email address and ticket no.
But if guest users use ticket no. incl. the prefix "#", login fails.
Suggestion: remove all non-digit-characters from ticket ID value
Side effect/Benefit: admin can add prefixes to any ticket ID like "#IT" in email templates while keeping the guest users being able to login (there may be several osTicket systems in parallel in one company, e.g. one for IT tickets, another for customer tickets; so you get a chance to know to which ticket system the ticket ID belongs to)