Administration side of WP 5.5 throw a Notice:

Notice:  WP_Block_Type_Registry::register was called incorrectly. Block type "core/image" is already registered

This is due to our code registering the "core/image" block a second time to add a render callback. See https://github.com/greenpeace/planet4-master-theme/blob/5ed59fe8122fe23c93a8373dcff41c022de25a29/src/MasterSite.php#L1103

Changing priority of our registration still raises the issue, provoked by the registration of core blocks by Wordpress.

I've made a proposition there https://github.com/greenpeace/planet4-master-theme/compare/fix/wp55-block-callback

We could also unregister/re-register this block, or find a different solution.