I'm 3.5 yrs post op at the same level with the replacement hardware and I have definitely had some bad days. I know when I sleep in the wrong position for too long, I wake in some pain. Usually it's when I wind up on my stomach trying to ignore the bladder alarm in the morning. Haha. Of course, this hasn't been a problem lately since I can't sleep on my stomach these days. I always attributed it to the fact that there are other levels of my spine that may become issues later in my life despite the ADR simply because there's degeneration and was concern at the next level above pre-op. Since it wasn't a pain generator, they decided to try to leave it as is.
The only other time I was in significant pain though... was when I single handedly moved about 90 PCs over the course of 1.5 weeks at work. This was done with a cart where I hauled 3-4 PCs at a time on the cart with several of them being moved multiple times during an space reconfiguration. There were a good 2-3 days during and then afterward all of it was complete where I hurt pretty bad. I don't think I would call it severe pain like pre-op though.
I'd think anyone who may have been worse off than I even was might have some weird flare ups like that. It's probably worth discussing with your physicians though, both PT and your surgeon. There might be some kind of alternate exercise path that can help or if there becomes a pattern of when it happens, maybe it's possible to avoid that specific type of motion.
During my own recovery, I played it super cautiously during the first full year even though I had a ton of success with the surgery and recovery. It drove my now husband crazy at the time because he knew how well my recovery went in the first few months, but I insisted on continued extra caution through that first year because of random twinges of pain I'd get. There were times I got concerned because of weird pain I'd feel after doing flip turns while swimming laps post-op but I'm pretty sure it was just part of the healing process. I'll test the theory again once I can fit into my swim suits again after our baby arrives.