Ok so I got a response from Apple on the feedback assistant.
They acknowledged the issue and said they are investigating and asked for a tonne of log files from my system. Either way. Don't think its getting fixed anytime before the next 12.2 stable update. Which would be atleast Jan/Feb.
Fingers crossed they figure it out and share information to actually fix it.
Response is quoted below:
**Quote**
We're actively investigating this issue, and would like you to provide some additional info & logging.
Is the issue only occurring with new Mail messages, or existing messages as well (old mail suddenly can longer be found after the update)?
Can Spotlight find other file types through the normal Spotlight UI?
After reproducing the issue, please do the following:
1. Rebuild the Spotlight index on your Mac following these steps:
https://support.apple.com/en-us/HT201716
Does the issue continue to occur? If so, please do the following:
2. Launch the Terminal application from the /Applications/Utilities folder
3. Enter the following in Terminal, press return, and follow the prompts (if any):
sudo sysdiagnose
4. When that has completed, please enter the following in Terminal, press return, and follow the prompts (if any):
sudo mddiagnose
5. When that has completed, please copy the following and paste it into Terminal, press return, and follow the prompts (if any):
mdls -s "`find ~/Library/Group\ Containers/UBF8T346G9.Office/Outlook/Outlook\ 15\ Profiles/Main\ Profile/Data/Messages/ | grep olk15Message | head -n 1`"
6. When that has completed, please copy the following and paste it into Terminal, press return, and follow the prompts (if any):
mdls "`find ~/Library/Group\ Containers/UBF8T346G9.Office/Outlook/Outlook\ 15\ Profiles/Main\ Profile/Data/Messages/ | grep olk15Message | head -n 1`"
7. When that has completed, please copy the following and paste it into Terminal, press return, and follow the prompts (if any):
mdimport -d3 -n "`find ~/Library/Group\ Containers/UBF8T346G9.Office/Outlook/Outlook\ 15\ Profiles/Main\ Profile/Data/Messages/ | grep olk15Message | head -n 1`"
8. Add the sysdiagnose and mddiagnose logs to this feedback report, along with the Terminal output from the last three commands.
Thanks!
**Unquote**