Lazyloading multiple instances

The same thing happens with JS when minification/concatenation is turned on.
Some JS code is executed multiple times.

could you please be more specific which JS’ being loaded multiple times ?

on my browser’s request list I didn’t see any duplication.

Its a problem with FSE and upcoming block based themes – as soon as I switch to normal theme everything is fine. This can be closed as that is an unreleased WP feature. Sorry to bother.

Found and fixed the issue – was related to the code from:
https://github.com/WordPress/gutenberg/blob/trunk/packages/block-library/src/table-of-contents/index.php regarding DOMDocument::saveHTML();
I was using a similar approach in my theme – you need to use LIBXML_HTML_NOIMPLIED constant to avoid multiple script tags (and also remove the generated Doctype)