Hi, My pella (Old) Sliding screen door.

It sounds like a problem with the spring mechanism. This is a small metal box in the door in which the latch itself goes through. Very often the spring inside this mechanism fails, which results in the latch being unable to do its job.

Unfortunately, we aren't able to replace either the spring or the mechanism that contains it. My recommendation is to contact Pella directly to see if this is something that they can assist you with.