I have a Kickr Core that is several years old. I ride with Fulgaz.
I’ve noticed that when I’m out of the saddle riding up a modest hill, pedalling is not smooth around the whole rotation. I’m doing 300W max, at say 60rpm cadence. It’s not a problem when seated though I don’t usually ride at such low cadence seated.
I don’t think it was always like this. Does it need some maintenance?
It seems better today, after I ran a spin down after my last ride. I don’t know if that makes any sense.
I should add that until this week, the Core hadn’t been used in over a month as I had been away on holiday.
I don’t know about the Core, but I have a 2018 (?) Kickr that was the last to still need spindowns. I will notice my resistence is off every couple of weeks, I run a spindown, and that solves the problem.
Oh, the Wahoo instructions recommend doing it every 2 weeks. Sometimes I probably go 2 years. 
https://support.wahoofitness.com/hc/en-us/articles/204281794-Spindown-Calibration-for-KICKR-v4-2018-earlier-models-and-CORE
I thought you were meant to warm it up before running the spindown, but the article doesn’t mention that.
I have a kickr V1 bike and swear that it’s harder and harder to make power. I’m just peddling through mush way more than I’d like to be. I wish there was a calibration that I could do. Wahoo seems to have disabled all calibration opportunities on their software.