Hi Ben,
I just got some time to do some thorough testing on this and I can confirm that the problem does’t present itself when I apply try this in Safari.
Back in Chrome where I usually do my web work, reproducing the issue is with a particular combination of columns and images. I was seeing this where I was using images from the Sample Woo products posts. As well as this the It only occurs when you use more then two columns (I tested with three columns and no more). Those images are dimensionally relatively large at 1000 x 1000 px and using smaller images doesn’t seem to trigger the issue I was experiencing. I did notice for the first time that when using the image block to access the media library that images don’t have the option to use thumbnail or medium sizes like in the old editor.
So it looks like this is specific to Chrome and rather an edge case that can be avoided. It also does the same thing if I use Row from CoBlocks and the equivalent from Qubely. I am also using the latest version of the Gutenberg plugin which may be causing some issues on the site that I using to test the new block editor. I did try to disable that plugin but whatever is the state of play with WordPress at the moment all my block editor pages go into error mode so I need to switch it on again.