Ads are shown after launching app but before window refresh

[Uni-verse]

Description:

Ads are shown after launching app. This is a regression on 1.66.x

Possibly an issue with the preloaded ad-blocking script not working

Steps to Reproduce

1. New install 1.66.x
2. Immediately navigate to youtube.com and other media sites
3. Play videos with ads for 30-40 secs until there is a black screen at the beginning of the videos
4. Look for ads / cookie notices in other tabs
5. Refresh the page using the reload button
6. Do the same for the youtube tab

Actual result:

Ads are shown until ad-block engines are compiled and user refreshes page

https://github.com/brave/brave-browser/assets/17885425/bcc0d00c-a4d8-407e-856c-e51bd9056737

Expected result:

Ads should not be shown

Reproduces how often: [Easily reproduced, Intermittent Issue]

Always

Brave Version:

1.66.90 1.64.x (intermittent)

• Can you reproduce this issue with the most recent build from TestFlight? Yes (beta)
• Can you reproduce this issue with the previous version of the current build from TestFlight? Yes (beta)
• Can you reproduce this issue with the current build from AppStore? No (new install)

Device details:

iPhone 12

Website problems only:

• Does the issue resolve itself when disabling Brave Shields?
• Is the issue reproducible on the latest version of Mobile Safari?

Additional Information

[kjozwiak]

The above requires 1.66.102 or higher for 1.66.x verification 👍

[Uni-verse]

Verified on iPhone 12 running iOS 17.3.1using version 1.66.110

• Ensured pre-roll and content ads are not shown on Youtube after launching Brave for new or existing users.
• Ensured content ads are not shown on media sites such as https://www.buzzfeed.com.
• Ensured ads are blocked using standard and aggressive blocking modes.
• Ensured that disabling Shields will display pre-roll and content ads on media sites.
• Ensured that are no issues after upgrading with several content filters enabled.

Example	Example	Example	Example

[Uni-verse]

Verified on iPad (7th Gen) running iPadOS 17.4.1 using version 1.66.110

• Ensured pre-roll and content ads are not shown on Youtube after launching Brave for new or existing users.
• Ensured content ads are not shown on media sites such as https://www.buzzfeed.com.
• Ensured ads are blocked using standard and aggressive blocking modes.
• Ensured that disabling Shields will display pre-roll and content ads on media sites.

Example	Example	Example	Example