YouTube ads are difficult to block with a domain blocker (i.e. Pi-Hole). YouTube serves the ads from the same domains as the content, with frequently-changing sub-domains. There is a very long running thread on this topic here: How do I block ads on YouTube?
For the ads on other sites, these tools are useful to determine the domains from which the ads are being served. This will help you determine which domains to block:
We cannot see that in a debug log. The log shows the configuration and operation of Pi-Hole only, and does not diagnose any network issues.
No. Once you make this setting change, it should be persistent and not change.
I don't understand this question.