Hello!
Probably the problem lies in the data that the browser accumulates. Over time, this litter starts to interfere with the extension! Don't worry, this is very easy to deal with.
First of all, you need to clear the cache:
1. Click on the three strips (≡) in the upper right corner -> "Settings"
2. In the window that opens, select "Privacy and Security" -> "History" - > "Clear History"
3. Check the "Cache" box and select the "time range to clear" at the top, click "Clear now"

Next, you should close and reopen the browser. Now try using the extension.
The problem persists? Then you should clean the site database:
1. Click on the three strips (≡) in the upper right corner -> "More Tools" -> "Web Developer Tools" (or press Ctrl+Shift+I)
2. In the window that opens, select "Storage" -> "Indexed DB"
3. Select folders in youtube.com section one by one and click "Delete"

Enjoy using YouTube Downloader!
It would be really great if you improve your score :)
Any additional questions will be gladly answered in our feedback service! It can be found at this address (unidownloader com/contact-us).
Best regards, YouTube Downloader (UDL Helper) Team.