Cannot type correctly when using certain input method in certain sites

When typing non-latin language using the input method, the first several characters cannot be type correctly.
I guess it is something about composition events.
https://stackoverflow.com/questions/51226598/what-is-javascripts-compositionevent-please-give-examples

I've tried fcitx chewing, fcitx mozc, ibus chewing, ibus anthy. All of them will fail like this:
https://imgur.com/a/NoG2cxT
When I want to type "da re", it splits into "d a re".

When I use the google-chrome browser it's all good.

How to reproduce
Use qutebrowser/Falkon or some Qt browser to view these sites:

• https://www.facebook.com/
• https://www.messenger.com/

And then use an input method (e.g. IBus, fcitx) to type something in any text field (e.g. comments).