Trouble with Morning Workouts

I guess there is always something new to learn.

I have started to do morning workout (never was a fan of them) and finding that even if my HR is low (which is what I train by), my RPE and sweat rate are much higher than I would expect.  I'm struggling to push hard enough to get the HR up.  I should probably test pace/speed to see if I am actually going harder, but it's on a spin bike, and there is no indicators other than RPE.

Anyone else see this?  Suggestions to adjust?  Go by RPE perhaps if it's a morning workout?  (which is sort of what I have been doing - since it's a struggle to get to Z2/Z3).

I'm wondering what is out of sorts.  My HR, or my perception of effort.