Your solution is failing because you are using a global variable counter to track the number of multiplications, and this counter is not reset for each test case. This causes incorrect results after the first run of the function.

Your solution is wrong, and tests are not at fault of your problem. If it's not the first time you encounter such issues, it would be a good idea to review your method, and not just blame tests. The "I. wrote. my. solution. first. in. VS. Code. The. results. were. all. correct." does not mean that your tests were correct, because, appparently, they were not. You did not tests whether your solution can be used more than once, and as it turns out, it does not and it breaks after a single use. You need to fix it, and reconsider the attitude of "EVERYTHING IS BROKEN!!1!1!".

You asked for a glib remark when you blamed the tests before having understood what happened ;)
Your code doesn't pass the example tests, and you can find those below the editor.
"Works on my machine" just means you didn't test the thing that failed.
If you still fail to reproduce those tests locally, then debug it in the codewars environment. I did look at your code and it is your code that is the problem, not the tests. Write it a little better please.

Ain't a great look to blame tests when your code is wrong xD