We have glass sliding doors for the bathtub. Today I noticed that the
inner most door is loose on one side. This side seems to have lost
connection to the bottom rail. This allows that door to be able to be
pushed inward. The other side of this door is still in the bottom track
and this side does not push inward. The door is fairly new (less than
1 year). I did not do the install (bought the house with it already
there). Are these usually adjustable? The door sits naturally in
place, but when pushed it has nothing on this side holding it to the
bottom rail. Any suggestions?

On the door at the bottom there is usually an adjustable track that can
be moved up or down. Or if the rollers are at the top, you can adjust
those. There are so many kinds of shower doors out there it depends
which one you have. But in general, thats how most of them can be
adjusted.