When I use the dedicated button to migrate from OpenNote by importing .json backup, I have the "check" animation but the app remains empty.

Here is a screencap, I couldn't explain better.
https://imgur.com/gallery/xwOU9e6

So far the workaround is to export each note (txt, md or html) manually from OpenNote... and to import them one by one in Kori.