__I checked that...__
Using the latest Material Insiders version, long codeblocks are pushed towards the navigation and table of contents sections, eventually hiding them. I've tested this with regular (non-Insiders) Material, and this doesn't happen. I'm not even using the latest toc.autohide feature.
Using Regular Material for MkDocs

Using Material for MkDocs Insiders
The first example still behaves as expected; problems arise as you widen the codeblock
The third example has the exact same content as the expected picture above



(It's a bit weird, because I can use toc.autohide, even though pip says I'm on 1.4.1 instead of 1.5.0)
theme:
name: material
custom_dir: theme
logo: assets/img/logo.png
favicon: assets/img/favicon.png
font:
text: PT Sans
code: PT Mono
palette:
- scheme: slate
primary: deep purple
accent: deep purple
toggle:
icon: material/weather-night
name: Switch to dark mode
- scheme: default
primary: deep purple
accent: deep purple
toggle:
icon: material/weather-sunny
name: Switch to light mode
features:
- instant
- tabs
- header.hide # Insiders
- search.highlight # Insiders
Thanks for reporting! I think I know where this is coming from. I’ll try to provide a fix asap!
Fixed in https://github.com/squidfunk/mkdocs-material-insiders/commit/701c008de92e958be98aeb75811b0704d5763670 – could you try the latest master? Regarding the version - I forgot to increment the version in the package.json, that 's now also fixed.
Great, it's now fixed. Thanks a lot for your efforts! ❤️
Perfect, thanks! Just released 5.5.13+insiders-1.5.1, which includes the fix.