GitHub probot : signature does not match event payload and secret

I am aware of this question GitHub Probot : ERROR probot : signature does not match event payload and secret. In my case the problem is a bit weirder. So when I'm running my application on the localhost and it is receiving github hooks via proxy https://smee.io/ everything works fine. But (with exactly the same env variables) when I'm hosting my application on kubernetes I got following error GitHub probot : signature does not match event payload and secret and I know that according to linked question it has something to do with Webhook secret but I do not understand why the same variable is working on localhost and give errors on k8 (ofc is in base64). My app is done according to documentation https://probot.github.io/docs/development/#use-server. I suspect that it might be connect with x-hub-signature-256 but it shouldn't be a problem since when I check Webhook secret on k8 pod I can see that it is correct. Any ideas what can be cause of the problem?