Slideshow & Tiled gallery blocks: Error uploading additional images

[chriskmnds]

I notice an error when uploading a second image to the Jetpack -> Slideshow block. This happens on WPCOM in both Gutenberg 7.2.0 (prod) and 7.3.0 (edge) to me.

Steps to reproduce the issue

1. Go to a block-editor post
2. Click on the block inserter and add a Jetpack -> Slideshow block
3. Click to upload an image (should work as expected)
4. Click to upload another image (should show error in console)

What I expected

Upload a second image to the slideshow.

What happened instead

Error.

Screenshots
If applicable, add screenshots to help explain your problem.

Uncaught TypeError: Object(...) is not a function
    at t.addFiles (editor-beta.js?m=1579787284h&ver=wpcom:2)
    at editor-beta.js?m=1579787284h&ver=wpcom:2
    ...

CC @ockham

[jeherve]

This can also be reproduced in current Jetpack stable without the Gutenberg plugin.

As a workaround, I was able to upload a new image using the Edit pencil icon for the block.

[jeherve]

This also impacts the Tiled Gallery block as reported in #14508 by @bindlegirl (good catch!).

2664014-zen

[kriskarkoski]

Drag and drop uploading also appears to be broken I suspect by the same issue. It opens the image in the same tab instead of uploading.

[tijosh]

Another report of this in #18016187-hc

[simison]

Looking at core gallery block might reveal what changes are needed. Some of the tiled gallery is modeled after that block so copying the file upload methods over might be good.

@pablinos mentioned on Slack that he could look into this at some point (p1581493933212600-slack-explorers).