I'm glad you got things sorted. I've worked in construction with a couple strong guys and they often used the "bigger hammer method" to solve problems, often exacerbating the situation. I can understand someone with your strength being careful. That makes perfect sense to me. I'll bet you've had to adjust how you approach things that come up in life's journey a bit. I gather you have some stories to tell. <eg> evil grinOk, last night I tried my Gillette Fat Boy again and got a smooth comfortable shave on setting #5 with Persona Platinum blade.
During the day I gave the razor several hot baths with dish soap, just to try and remove any gunk or debris from internal mechanisms that may be causing stickiness. When I loaded the razor blade, I carefully twisted the door closure knob until it seemed to hit a 'soft' stop, for lack of a better term, then I continued to twist harder against stiffer resistance until I hit a 'hard' stop, where I could turn no further. I don't know if it was the half-turn specified for locking, but it wasn't very far, so that's probably about what it was.
When shaving, I didn't perceive any whisker tugging or blade movement as I did on earlier shaves reported at the beginning of this thread. I still need to test a few more times to confirm performance will remain consistently better, but it seems this may have solved my problem.
Apparently, in my fear of breaking something by twisting too hard, I was just twisting knob to the 'soft' stop and not going any further, so then the closure and blade clamping was not in a fully 'locked' state, thus leading to looseness or movement of the blade during shaving.
I really have broken a lot of things (not razors) in the past with my brute strength of over-tightening, so that was the source of my hesitance to get too aggressive with tightening TTO knob. My dad used to say: "that kid could break a sledge-hammer with an iron handle" about me, so something I'm famous for I guess.
Thank you to @CCS, @luvmysuper and others who provided guidance and helped me resolve this issue.