On WordPress Multisite, Icon Block (and other Ghost Kit blocks that store SVG in attributes) can break after save for Editor users. After updating the page, SVG is removed from block attributes, and Gutenberg may show “This block contains unexpected or invalid content.”
This is WordPress security sanitization (KSES) on Multisite. For non-super-admin roles, SVG markup is filtered when the role does not have the unfiltered_html capability.
To fix this grant unfiltered_html to the affected trusted role on that Multisite network/site (commonly Editor, sometimes site Admin), then re-save the page content. This prevents WordPress from stripping SVG used by those blocks.
Reference issue: https://github.com/nk-crew/ghostkit/issues/114