Memory leak issue on iOS 12.1

[MainasuK]

I have a singleton to manage instance of Erik.
And after complete task I release the instance but Erik still in memory.
I use two Erik instances visit www.apple.com and found about 50MB memory leaked.

My app has not refer the instance anymore. So I think it's could be leaking somewhere. Maybe due to WKScriptMessageHandler.

Demo app: https://www.dropbox.com/s/luyes5cbz03jg0k/ErikDemo.zip?dl=0