My extension is supposed to work with https://web.whatsapp.com/:
"content_scripts": [
{
"matches": ["https://web.whatsapp.com/"],
"js": ["entry/content-script/cs.js"],
"css": ["entry/content-script/zen-mode-ui.css"]
}
],
When I load web.whatsapp.com directly, in a new tab - all is fine: the stylesheet is injected like it's supposed to:

But! If I first go to whatsapp.com and there click the link to Whatsapp Web - when web.whatsapp.com loads, the css is NOT injected:

There is no injected stylesheet snippet.
Although, the content script loads just fine.
If I then refresh the page - all is good.
Is it a bug in chrome extensions engine itself?