Hi,
The "two-pi-hole-instances-one-with-failed-to-send" issue is currently open in the NLnetLabs forum.
I have a question related to the latest NLnetLabs version (1.22.0) and the latest version for Bookworm (1.17.1).
I don't want to break my current set-up therefore my question here is if it is advisable to install 1.22.0 to see if it solves the unbound issue we are seeing?
Thoughts...
Steen
That would only make sense if unbound developers have decided that they would need to improve their handling of TCP pool exhaustion and already have supplied a patch that would haven been released with 1.22.0.
Related questions should be answered by unbound maintainer's.
If 1.22.0 contains a related patch, then it would depend on your willingness to test that release, based on the current urgency as personally perceived by you.
If increasing incoming-num-tcp in unbound.conf has mitigated the issue for you, then it would be perfectly fine if you prefer to stick with your current installation. 
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Read the changelog, check if something has changed that would solve the problem. The changelog refers to the current GitHub master, not the downloadable version (v1.22.0)
Be aware replacing the bookworm version with a compiled version of the github repository doesn't work, you'll need to rebuild the system (learned the hard way...)
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@jpgpi250
Thank to both of you!
My question was just to get an opinion from the Pi-hole forum members.
I might check the changelog ...and I am not keen at all to might have to rebuild the system. 
I'll let others at the unbound forum where I raised the issue upgrade to latest version.
Take care - Steen