Ok, so I got it working again. My iPhone is my personal phone, but I also put work stuff on it. My employer installs a Blackberry UEM profile so that all my work-related apps are secure from the rest of the phone. BB apps are pretty bad, but it keeps things fairly separate and I don’t really have a choice (unless I want two carry to phones, which I don’t). Anyway, when I deleted the BB UEM profile, reminders through Siri on Apple Watch started working again. A very weird bug as iOS Reminders app, Siri, iCloud and the Apple Watch do not have any interaction with the BB apps as far as I know. I now need to get BB put back on my phone later today, so fingers crossed that it doesn’t break reminders again.