asdrt Sadly, I don't think there is any solution. The problem lies in the code of this Shitapp™ made by the retarded company Crapbook™. I have another Android phone with the stock OS installed with all the "google certifications", all the Play Services installed and whatsapp installed from the official website, and it still failed to ring sometimes when the device was sleeping. It does not matter if one uses the proprietary implementation of notifications or google's firebase notifications. The problem persists anyway. So clearly this is not a GOS issue.
Also, to prove my point even further, this feculence of an app is so poorly coded that it can barely be used with memory tagging enabled, since it crashes every other time one opens it. God only knows what memory shenanigans are there under there.