Glad it helped you think more about it @Alex, that was my goal with starting the thread!
I’m in a similar boat right now, and that’s with taking it easy in general. I was doing a hard group ride and I could tell at the first sprint things weren’t great - couldn’t even come out of the draft of the guy initiating the sprint. I know he’s strong, so I didn’t worry too much, but it was a data point - lookin later the power was no great shakes. 2nd sprint point didn’t go great, but didn’t seem egregiously bad - also no great shakes looking afterwards, but I decided I’d pay more attention next sprint. 3rd sprint - I miss the boat on the guys who jump, so I’m going all out, and I look down and my power is like 450W. This was after maybe 10 seconds, I wasn’t necessarily expecting something amazing, but I know I can do more than that. Then 5 minutes later I’m just dangling behind the group when it’s going sorta hard, and I feel like I’m a 9 outta 10, and closing a 10 foot gap seems like it’s gonna be a challenge.
So I pulled the plug, and road in easy, cut my next 4 hour sessions to a 2.5 hour cafe ride, and took 3 days off. The old me would have just put my head down and powered through the rest of the ride and scheduled some killer workout for Tuesday or Wednesday.
My libido had also been in the tank, which I think is another great sign that maybe you are overcooking it. Yeah, I know, TMI. 
Even when you are working to not overdo it, you can overdo it. I’ve had a few big training weeks, I did a 3 day Omnium, and 2 sets of practice crits and a race the last 2 weeks after that. So lots of intensity.
Also, last year around this time I was flying, but then the fitness sort of went away for a bit. This year I’m going to try and get ahead of it, I have a little break from racing before hitting it hard, going to try this break now.
Oddly, my HRV was looking good, but has gone the other way these 3 days off. Heart rate on the other hand has been very low recently. More interesting data.
You gotta learn your signs and figure this out. A coach can certainly help.
I think the biggest trick is not to fall into the “holy crap, what’s happening with my fitness, I better train more!” trap.
Anyway, I hope all these details resonate with people. You gotta figure out what will keep you consistently riding the bike. And not getting too over-cooked is the biggest thing I’ve learned coming back. I’m now on my 3rd year of consistent riding, something I never managed back in the day. I feel like my fitness is as good as when I was 20-30 because of it. And that I probably squandered a lot of my talent back then overtraining. Live and learn!