High PE combined with low HR = overreaching which can turn into overtraining if you keep it up. High HR during high PE is what's normal.
Yes, if your HR won't go up, the thing to do is back it way off and just toddle along. And yes, if you don't have one or two 24" box fans blowing on you, you're doing it wrong. They should be strong enough that you need cycling glasses. Since I'm indoors, I'll frequently ride shirtless if it's over 60° - I ride my rollers out in my shop with the winter temperature usually around 50-55.
You might try doing most of your training rides steadily at VT1 (first ventilation threshold). This is the point at which your deep steady breathing would rather suddenly become faster if you increased your effort and heart rate. You should be able to recite the alphabet, maybe twice in one breath at or below VT1. My VT1 is at about 75% MHR. Yours may be different. A steady 1-1.5 hours at that threshold is very good training. Try only two Zwift races/week.
The weakness in the left arm is a bit worrying. If you feel pain there, quit and maybe call 911, eh?
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