Many, if not all, gun companies say "Don't use reloads in the gun." The idea is that if you use a poorly reoladed cartridge and blow the gun up, don't blame us.
Which is fair enough.
Glock really makes a fuss about it. That and not using lead bullets (Though countless people do, and you can buy "lead friendly barrels".)
As the only trouble I have ever had with my Glock 17 was because of a reload, I don't do it.
If you are using jacket reolads, it isn't always cost effective to reload 9mm rounds anyway. But that is a personal call.
Chamber designs are also an issue. Some designs don't fully support the shell when it is fired. Too much to get into, but that can make the brass weaker.
Millions use reloads without harm every years.