I have one of famous Prevue F040 (I believe) that I roll around the house a lot. The bottom tray doesn't stay in place anymore (and, for some reasons I don't bother to use a grate on the bottom so it's just a tray, my birds are never on the bottom anyway) . The tray falls down on one side, making a gap at the bottom of the cage
Today I uncovered my birds and was shocked to see there were only 8 of them in the cage. I have a habit to always count my birds before I cover them for the night - just in case. Didn't I count them yesterday? Did I lock one accidentally in a cabinet? Did he make his way out of the house and I didn't see it? I started to panic. Then, I heard a weak chirp.
Tater Tot was found in the bedroom where they spend a night, sitting on the curtain rod, thanks goodness! He looked scared, but then he was fine when he joined the flock.
He obviously made his way out thru that gap on the bottom during morning hours after I got up and left the bedroom at 6.30. I fix the tray when they go to sleep but in the morning it was partially down again.

Any suggestions? I will put bottom grate into the cage but it's still annoying that bottom tray doesn't stay in.
Oh, sometimes a wheel pops out of its slot when I roll the cage. This is easy to fix though

Would it be possible to wire the tray into position or put something under it to hold it in place? I can't tell what's causing the problem so I'm not sure what the solution would be.

thank you Carolyn.
I can tell that the lower part of vertical poles is very wobbly and unstable, they don't stand vertically anymore. this is causing distance between the poles that hold the tray to be incorrect for the tray. I installed the grate and it helps a lot to keep the poles standing correctly
I will ask my husband to look at it this evening.
But not finding a bird in the morning was definitely a shock LOL

You might be able to use wire or some kind of metal brackets to hold the pole in place.

Drill hole n zip tie it.