It doesn't says both are valid, it says one digit can belong to two adjacent digit-pairs.

We define a digit-pair as: Two digits with at least one question mark between them.

Your task is to check if there are exactly 3 question marks between every digit-pair and their sum equals to 10. If so, return true, otherwise return false.

For that string your code should return false, as the similar sample test shows.

I solved the kata in JavaScript, so I am able to see your code. Your code passes the first sample tests, but fails in some of the series

  it("Special cases (splits at start/end and overlapping splits)", function() {

for example

    Test.assertSimilar(splitWithoutLoss("aaaa", "|aa"), 
                       ["aa", "aa"])

I don't think it works fine in VSC either.

FATAL ERROR: CALL_AND_RETRY_LAST Allocation failed - JavaScript heap out of memory

This means you are using too much memory (you are probably building a gigantic array or something like this, or a part of your code keeps pushing value into something and never stops), and it is not a kata issue.

Advice: your while loop is probably the culprit. You are probably not testing your code with the same input in VSC as here. Please refer to the documentation: https://docs.codewars.com/training/troubleshooting/