So, Youtube videos either never start, or take forever to start, or take a reload or two to start, or play for a few seconds/minutes and then timeout/connection lost/stop playing.
In the Query Log on the GUI, the culprit is always (some random text).googlevideo.com that is being blocked.
I have put googlevideo.com on the Whitelist, and googlevideo.com is not on the Blacklist, according to pi.
I cannot wildcard *.googlevideo.com on the Whitelist, as it doesn't take wildcards.
Sometimes, it works. For example, this very moment, I was watching a Youtube video, and "r2---sn-a5meknll.googlevideo.com" showed up in the query log as "OK" and the video played. For about two and a half minutes. At which point, the video stopped, eventually dropped a connection refused/lost error message, and the log shows "r2---sn-a5meknl6.googlevideo.com" is blocked.
You have a very large number of blocklists, and malformed entries for blocklists:
https://raw.githubusercontent.com/EnergizedProtection/block/master/ultimate/formats/hosts.txt
https://raw.githubusercontent.com/crazy-max/WindowsSpyBlocker/master/data/hosts/spy.txt
Whitelisting Suggestions for Pi-Hole
https://raw.githubusercontent.com/StevenBlack/hosts/master/hosts
https://mirror1.malwaredomains.com/files/justdomains
Plaintext and comments should not be in the lists. You need to clean that up.
In the mean time, try http://pi.hole/admin/queryads.php and do a partial search for the domains being blocked, there is a strong possibility that one of your lists is blocking, or one of the lists is not formatted correctly and is causing other issues to come up.
pihole -q -all r2---sn-a5meknl6.googlevideo.com
Match found in list.7.jasonhill.co.uk.domains:
r2---sn-a5meknl6.googlevideo.com
Match found in list.38.smokingwheels.github.io.domains:
r2---sn-a5meknl6.googlevideo.com
r2---sn-a5meknl6.googlevideo.com
Pi-hole will do exactly what you ask it to do, and in this case you are asking it to block what you would like to see.
Thanks. Deleted all of my block lists and re-added from a collection website, and made sure all were valid, no comments in my sloppy copy-and-paste, etc. Still blocking 2.5mil domains, but now none of the [gibberish].googlevideo.com sites are included.
As you have discovered, grabbing blocklists from the internet in quest for a higher number of blocked domains can cause problems. The more block lists to which you subscribe, the more opportunity for one of the block lists to include something that you don't want blocked. I run just the basic 7 block lists with a few dozen added regex filters and see zero ads.
My advice would be to use a small number of blocklists, then add local blacklist and regex to fine-tune your Pi-Hole to your specific needs.
All of the domains like the one shown below are an attempt to block YouTube ads. They may work for a short while, but then the domains change again and the block list interferes with your content.
r2---sn-a5meknl6.googlevideo.com
If you do a search for just "googlevideo.com" in your gravity list, you may find quite a large number of these in there.