Aluminum Anti-Seize - Suctioned Bottle

The aluminum anti-seize (Permatex) that I have had for several years has suctioned the bottle (Sides bending in a lot). I haven’t used it for over a year so I don’t know when or how fast this happened.

Does anyone know why this happens and if the anti-seize is still good?

UPDATE: Reached out to Permatex and got the following response. They didn’t know what caused the shrinkage, but did state that it has a "3 year shelf life" and that "If the product is still has good consistency then it is okay to use, if it has stiffened up, try adding a little mineral oil to it." I am going to continue to use what I have since mine still seems to have the same consistency.