"Undefined" text appears in the first column when I publish and re-edit a post/page

[andreiungurianu]

For some reason, when I create a new column and row in Gridable, publish the post, and then go back to edit it, there's a text that gets added to my original text—"undefined"

Here's a video that shows what happens: Undefined text appears in Gridable.mp4.zip

If I hit publish again, another "undefined" shows ups in the first column:

I'm using Gridable Version 1.2.9, Pixelgrade Care v1.7.12, WordPress 5.5.1. This happens when I use Rosa1, Noah, and Osteria, so the theme does not seem to cause the issue.