Custom CKEditor shows blank when editing collection entry

System Information
  • Strapi Version: 3.4.6
  • Operating System: Win 10
  • Database: MongoDB
  • Node Version: 14.9.0
  • NPM Version: 6.14.8
  • Yarn Version: 1.22.4

I followed the official guide how to replace the default RTE with CKEditor. So far so good - the editor is replaced, I can create RT content and I’m able to see it on the front end. The problem is when I want to edit an entry in the collection - I click on an entry and CKEditor appears blank. As if there’s no content in there.

One thing I noticed - if I click on the MediaLib button above the editor and insert an image - all the content appears, with the new inserted image in the end. So my guess is (and really, I can only guess here, I might be wrong) when I edit an entry, some onChange method is not being called immediately, only when I insert the image from MediaLib. Though it does not happen if I start typing text.

Any idea how to make make the content appear immediately when I want to edit an entry?