Created attachment 342023 [details]
Project to reproduce the issue

To reproduce the bug:

1. unzip and open the project in Xcode 9.4
2. run the app using iOS simulator 11.3
3. click on the text "testing"
4. type about 15 lines or so with multiple words
5. On the last line with multiple words, select the entire line
6. With the line still selected, try to scroll upwards

Expected
Able to scroll up

Actual
The scrolling keeps jumping back down, as if to keep the selection in view. Even after removing the selection, scrolling upwards still keeps jumping back down.

Screen recording:
https://cl.ly/2e1j1P0D2h0u

Additional details

The issue doesn't happen on iOS 11.2, only 11.3 and 11.4 currently.

In the attached zip file, the view controller creates a WKWebView instance that loads the following HTML string to construct a contenteditable div.

        let html = "<div contenteditable=\"true\">Testing</div>";
        webView.loadHTMLString(html, baseURL: nil)