I can confirm that this is somehow tied to a YouTube account which is why it doesn’t happen for everyone. I have the same problem and I’ve tested this on three different browsers: Vivaldi, Brave, and Google Chrome (with uBlock Origin).
On all three, YouTube had a 5-10 second delay before videos started playing if ad blocker is enabled.
The issue goes away and videos start loading immediately if you do one of the following:
- Log out of YouTube and use it without an account
- Switch to another account
- Enable a VPN
I would think it’s account specific targeting related to adblock usage since switching to anotoher account fixes it, but that doesn’t explain why enabling a VPN also fixes it too..