Key only playing when they like to

Hello, I already made a thread about the melodica faili g on me and how to clean and maintain it. The last time I cleaned it three times in a row and it failed to me on the first try afterwards.

Now as a next test I ran boiling hot water through it(do not recommend, I burned my fingers). This made me play it again... for about 5 Minutes and it started failing again. I made a video maybe somebody can see what could be the issue.

In my other thread it was said it could be a climate issue or me using the valve not often enough. But why is it the low d always and the keys around it sometimes? And NO other keys failing? The higher and lower notes literally never fail and always play. How to clean it to make no keys fail?