Certain CSS(?) elements break on two specific websites.

[ghost]

Description

On two websites, 4chan and Youtube, CSS elements break between tabs. Sometimes refreshing fixes the issue. On 4chan in particular, the auto-update and linked replies no longer work until refreshed, which seems to be tied to the buttons being missing.

On youtube, sometimes it will ignore the "Dark Mode" preference. Toggling it again will fix it, refreshing does not.

It should be noted on these two sites, sometimes the ad blocker fails to remove the empty frame of the blocked ad. I've noticed this on other sites as well.

Steps to Reproduce

Visit any thread or page on 4chan and Youtube (while logged in).

Actual result:

4chan in particular in Brave (sorry about the somewhat vulgar ads, although these should have been blocked):

Expected result:

Example of the same page in Microsoft Edge, note the missing elements:

Reproduces how often:

I would say this happens around 90% of the time a thread is opened from 4chan, and around a 40% chance depending on how long Brave has been open for Youtube's Dark Mode to break.

Brave Version

about:brave info:

Brave: 0.20.46
V8: 6.4.388.41
rev: 5eb035c
Muon: 4.8.2
OS Release: 10.0.16299
Update Channel: Release
OS Architecture: x64
OS Platform: Microsoft Windows
Node.js: 7.9.0
Brave Sync: v1.4.2
libchromiumcontent: 64.0.3282.140

Reproducible on current live release:

Yes, this is the live build grabbed from Brave's website for "retail"

Additional Information