Hi Martijn,
Thanks for the reply.
Yes, I've enabled bot filtering on all views except my unfiltered view. My site gets so much bot traffic that the data would be unusable without it.
As for filtering the traffic, I'm not aware of any way to retroactively filter out User-Agent unless I use GTM to create a custom dimension as described here: https://www.addsearch.com/docs/analytics/addsearch-bot-google-analytics/
Perhaps this is something I should do in case something like this ever happens again in the future.
I'm still hoping for other suggestions - particularly ways to ask the Google Analytics team to include "whatstuffwherebot" as part of their bot filtering.
Best,
Akira