Sounds strange if it's also on Android. Doesn't seem to be device-specific. I can't find another app to test it on. Chances are those apps are also webapps or using qtwebengine.
I have select (context menu) issues as well on Oneplus 3.
As long as the text is editable i.e. text input areas, you can select things with long press on the spacebar. But it does seem that there is an issue here. Maybe file another bug report?