When testing my skill, I call something like "Say cat in french," which I know will work. It says "cat is chat in french" for example.
Then I try something that I know won't work, like "say sfhskfjh in french." This returns "Remote endpoint can't be called", as expected.
But then, when I try "Say cat in french" again, I get the remote endpoint error until I re-upload and save the code (without changing it).