YouTube has been making regular changes to their policies in regards to monetization and advertiser-friendly content. Due to the amount of videos uploaded on a daily basis to YouTube, YouTube has to use several different processes to review videos, which can be automated or manual. Usually the videos are first checked using an automated process, which is not perfect, but a work in progress. However, it's possible that some times these reviews are not as accurate as they could be and they require a manual review to properly classify a video.
For the latest updates regarding monetization and advertiser-friendly content, please check this article.
What does it mean?
The yellow icon indicates videos are still eligible to earn money in YouTube Premium, but will have limited or no ads because the video has been classified as either not suitable for all advertisers, or has been fully demonetized because YouTube believes it doesn’t meet the Advertiser-friendly content guidelines.
How does the appeal process work?
If you believe that your video was incorrectly classified, follow these steps:
Eligibility for appeal
Why does my video monetization icon keeps changing from Green to Yellow back-and-forth?
This can happen because YouTube's automated system repeatedly scans each video using the latest information available, which may cause the system to change its decision. If you feel the yellow monetization icon was an error, you can submit an appeal directly to YouTube.
Do you have any recommendations/tips?
Here are some resources that you may find useful to correctly monetizing your videos:
Creator Blog post on advertiser-friendly content guidelines
Creator Academy lesson on creating advertiser-friendly content
Forum post on appeals process
Note: Video classification may change due to continuous reviews YouTube makes, even if it was initially classified as suitable for all advertisers (green icon).