Though I've never gotten my bike fit "professionally", I did get them fit by a person who does the professional fitting, not extensively however.
Recently, I hit a nasty bump and my seat post dropped. I tried restoring the setting but the tape that I used to mark the spot moved and I kind of had to re-adjust the saddle height using the "feel" factor.

After adjusting the saddle height, I noticed 3 changes.
1. Thigh burning - Muscle above the kneecap to the inside, the "teardrop" muscle?, burns significantly more than before whereas I rarely felt burn there before. Also the big mass of muscle on the upper and to the outer side of the thighs don't burn anymore, which is usually the place that I felt burning when I would push harder.
2. Calf muscle - Lower part of my calf muscle, between the big mass of muscle below the knee and above ankle, is sore today after riding yesterday.

3. Lower back soreness
After about an hour of hard riding, the lower back was definitely feeling strained with soreness. Perhaps this isn't the saddle height issue because the muscle or tendon behind the armpit area where my limbs are connected to the torso was hurting quite a bit as well. I was riding a very rough road with lots of "pop" in the drops and I rarely ride in the drops for that extended amount of time.


All of this I guess means I'm using set of muscles that I wasn't using before. I don't really notice drop in power numbers.
The leg and body angle looks okay and heel to the pedal is good as well.

I'm wondering if my fit before was too low and I've just gotten used to that or I'm feeling changes as a common symptom to saddle being too high.

Muscles burning? Obviously you fubared the aerodynamics of your S5, gunna have to trash it and start over

have you tried lowering it? sounds like it's a little too high. But I am far from anyone who should be giving fit advice...

Mine was a bit (and I stress a bit) to high and gave me some lower back issues. I would also get a little knee pain upon the bottom apex of the pedal stroke.

Is your seat straight? having it off center may twerk your back a little as well.

YouTube how to do your seat post fit to get a general ballpark and go from their is my suggestion.