I attended my first event with the R1 this weekend, despite owning it for a couple of months I've only used it at parkruns and a couple of other personal events in that time.
I was photographing Hyrox in Manchester on Friday, Saturday and Sunday.
Just before the event I'd ordered 2 new Manfrotto CF Express cards, as I've found them to work well and good value for money, but when I started on Friday evening the camera seemed to be freezing after taking a burst of images, when I had a gap in participants I took the Manfrotto card out and replaced it with one of my existing Sandisk cards, same was happening with that card as well.
After a bit of head scratching it turned out, after applying a firmware update, it looks like image review was turned back on and set for 2 seconds, so as I was doing a short burst it was trying to show me the last image for 2 seconds

It probably sounds stupid, but when you're in the thick of it, and you've got an arena full of participants, it's hard to realise the obvious until you've had a second to compose yourself and really think about it.

It took me around 15 minutes to realise what was going on.
It was a long weekend, 4 hours Friday and 15 hours each on Saturday and Sunday, but over the weekend not only did I get to put the R1 through it's paces, with 45,000 images taken, I also got a chance to use my 2 new lenses and really test them, the RF 24-105mm 2.8Z and RF 70-200mm 2.8Z, and both were amazing as you'd expect.
The lighting in the arena is shockingly bad, so I knew it was going to be a good test for the R1's low light capability, Friday and Saturday was easier as I was using the RF 15-35mm and was very close to the subjects so I used a hot shoe mounted LED light, but Sunday when using the 24-105 and 70-200 that wouldn't have been any use at all.
None of these images have had any noise reduction applied (apart from Canon's own in camera as they were shot as JPEG).
Friday - Canon R1 with RF 15-35mm 2.8 plus a small Godox hot shoe mounted LED light
ISO 8000
ISO 16,000
ISO 25,600
Saturday - Canon R1 with RF 15-35mm 2.8 plus a small Godox hot shoe mounted LED light
ISO 20,000
ISO 25,600
ISO 40,000
Sunday - Canon R1 with RF 70-200mm 2.8 Z and no additional lighting
ISO 20,000
ISO 25,600
ISO 40,000
Sunday - Canon R1 with RF 24-105mm 2.8 Z and no additional lighting
ISO 20,000
Before anyone says, I know they're not perfect, not by a long shot, but in this particular arena, with the lighting being as bad as it is (and the organisers don't really like you using flash) you can only work with what you have, and the R1 definitely made it easier.