same issue here, although i went quite far to clear up the web view, and delegates and attached config after done with web view, still its kept in memory.

What I see is that SecTrustEvaluateIfNecessary is causing this. Which means a deadlock to my understanding: unless you figure out how to override certificate trust check of WKWebView to do it in background thread separately from loading web view url (needs to be on main thread).