Block Switched to Tiled Gallery Doesn't Show Images

[ChrissiePollock]

1. Open a post or page editor on any site.
2. Insert a Gallery Block and add some images.
3. Select the option to Change Block Type or Style.
4. Choose Tiled Gallery.

What I expected

I expected the gallery to show in Preview.

What happened instead

The images didn't appear in the editor until I clicked the empty boxes. Even then, they still did not show up in Preview in Firefox or Chrome. When I switched the blocks back to Gallery, they showed. When I added the Tiled Gallery as the initial choice, the images showed in Preview. Just not when the block was changed to Tiled Gallery from another block.

When I added the Tiled Gallery (which worked as expected) then changed it to Gallery then changed it back to Tiled, I lost the images again, and they did not show in Preview.

Also, sometimes in Firefox, the Block settings would start flashing. It did not do this in Chrome.

This is similar to #45138, but it's in the editor itself, and not in the comments.

Screenshot / Video

Chrome screencast - https://d.pr/i/QMP2wj

Firefox screencast - https://d.pr/i/7zNr8R

Flashing example (it's a lot faster than the recording shows)

Context / Source

#manual-testing

[sdixon194]

Another report in 25466222-hc

[carladoria]

there is a similar issue in 26867253-hc but user ghosted out before I could ask more details. In their particular issue, each time they used the Tiled Gallery, they would get an error an "attempt to recover block" which will turn out into an empty Tiled Gallery after re-entering the page. I'll dig deeper into this and might report a different bug, as it is not exactly the same issue, but seems heavily related.