There are a few different reasons why a key binding may not do what you expect, which range from something stealing the key on you to a package rebinding it unexpectedly to something else and even keyboard layout problems in which Sublime doesn’t see keys as the keys that you’re pressing.
In order to diagnose which of those it is (if any) it can be helpful to turn on input logging with
sublime.log_input(True) in the Sublime console (
View > Show Console) and potentially also
sublime.log_commands(True) as well. The first tells Sublime to display in its console what input it sees you entering, and the second tells it to log what command (if any) it’s executing as a result.
Using that can help determine what might be going wrong. This is also illustrated in more detail in this video on diagnosing key binding problems.