Received Hash and generated hash not matching at times

[jts74]

Using accept.js with php. For a small number of transactions, the hashes do not match. The transaction ids and amounts all match and the charge goes through on authorize.net. What could this mean?

[naivysr_2018Dev]

I'm having the same issue. 

In my case I have a webhook set up. Once we receive the request we generate a hash using HMAC-SHA12 and our signature key and then compare the result with the X-ANET header hash sent.

Sometimes it matches, sometimes it does not. This only happens with production credentials, not sandbox. I've even taken the request body, hashed it online with a tool auth.net recommended and it te result matches the one I generated but not the one they sent. 

Would there be any configuration that's triggering this?

Thanks