"Functionality issues" refers to problems or flaws in the way something functions or works. It indicates that there are difficulties or problems with how a particular thing is supposed to operate.
Sentences with «functionality issues»
* Fixed loss of functionality issue that would occur when two crates were stacked if player attempted to capture bottom crate. (mkaugaming.com)
Parents who dislike this monitor complained about having functionality issues with the units. (omaby.com)
These updates are included to address functionality issues not related to the security of Pixel devices. (9to5google.com)