Jetpack Boost 1.9.3: Images and other elements not loading unless logged in

Impacted plugin

Boost

Quick summary

Initial report in 6493580-zd-woothemes (Requested a follow-up in 6493764-zd-woothemes when this is resolved.)

With Jetpack Boost active and updated to 1.9.3, images on the site fail to load unless logged in. User and I confirmed this was replicated in multiple browsers and devices (though only when un-proxied).

EDIT: Other reports have come in where this has affected other elements, including slideshows/carousels, mobile menus, and the cookie and consent banner widget.

Steps to reproduce

Activate Jetpack Boost 1.9.3 on an Atomic site
View the site

A clear and concise description of what you expected to happen.

Images should load as expected.

What actually happened

Images all fail to load. Browser console showed a few repeated errors for a /_jb_static/... file failing to load.

Impact

Some (< 50%)

Available workarounds?

No and the platform is unusable

EDIT: Clearing the site's cache in CLI has been shown to resolve issues. Deactivating Jetpack Boost is a temporary solution otherwise. There is no need to downgrade to a previous version except for troubleshooting purposes.

Platform (Simple and/or Atomic)

Atomic

Logs or notes

I've been unable to replicate this myself so far, including on an AT test site using the same Seedlet theme and similar plugins. The customer did report that the issue started today (July 3) and was resolved on deactivating Jetpack Boost.

Checking with this customer now to see if they'll consent to us reactivating Boost on their site temporarily to get more details. Creating this issue early in case other reports come in before we hear back.

Automattic / jetpack