Interesting...
Continued searching on the web and here on discourse and found the following:
- Default blocking behavior makes Chrome slow · Issue #4107 · pi-hole/pi-hole · GitHub
- Consider making NODATA the default blocking strategy
I applied the "fix" by setting BLOCKINGMODE=NODATA in /etc/pihole/pihole-FTL.conf (more details about BLOCKINGMODE here: https://docs.pi-hole.net/ftldns/blockingmode/).
From the discourse and github I understand this seems to be a MacOS bug however I experienced the slowdowns on non MacOS devices as well. After I set the BLOCKINGMODE=NODATA I don't experience the slowdowns anymore. I will continue monitoring my network but this seems to be the fix!