The two panels aren't aligned, I'm surprised that the door still slides.
By the looks of it, this is a wired glass door, so it's not exactly new. Replacement may be warranted. (20+ trouble free years isn't a bad run)
Who do these tenants think they are expecting the windows to open? Fresh air and ventilation are much overrated ;)
Hint: if they can't open the windows you can't complain about mould.