Notice the 2nd paragraph shifts for about 1px.
In comparison, here’s the UX in iA Writer:
I work on frontend development, and I know how difficult i18n is. Bugs like this just happen all the time. Sometimes, there is just no way to continuously test the app except for regularly using it.
For this reason, I think iA writer has and will continue to have better support in CJK. In case you don’t know yet, iA writer is developed by a Japanese company. If there’s an issue with CJK, the development team will likely catch it before the users.
If you write in CJK, this may be a factor to consider.