Blood pressure measurement - automated vs manual method

I am not finding any information on my specific problem, but thought that someone here might understand.

I admit that I'm overweight. My upper arms are quite fleshy and flabby. I have also been a regular blood donor for my entire adult life. I've donated blood about 150 times.

The problem started about 10 years ago. I went to donate blood, as usual. But, for the first time, the donation center was using automated blood pressure machines, rather than the hand-pump and stethoscope method. During the measurement, the machine paused, released some pressure, then increased the pressure enormously - to the point I was almost in tears from the pain. For the first time in my life, I was about to be deferred for high blood pressure. But my blood pressure had always been on the low side, never even approaching a high number The nurse took my BP manually, and it was easily in the normal range. And the difference was not small. The manual method said my BP was something like 107/75, the automated machine said it was something like 185/105.

I continue to have the same problem with automated BP machines. If I go to the doctor's office or to a blood donation site where the machine is automated, the reading is extremely high (after crushing my arm). If my BP is taken manually, it is in a normal range. Again, not a small difference - readings of 180-200 for the upper number with an automatic machine, readings of 115-130 with a manual cuff.

Nobody believes me that this happens, unless I'm in a place where both methods are available. It always surprises practitioners that the automated machine is so inaccurate. Please remember that the practitioner can actually hear my heartbeat with the manual measurement, so it's clearly the automated machine that is wrong. It seems that the automated machines have a hard time detecting my pulse, which is why the machine increases the pressure to the point of extreme pain.

To answer the obvious questions - yes, they use a bigger-sized cuff. Yes, I sit with my feet flat on the floor. Yes, my arm is resting at heart level. No, I'm not talking while the measurement takes place. Yes, I do get frustrated when the person taking my BP doesn't believe me that the machine is wildly incorrect. No, this is not white-coat syndrome, or why would it not appear when I'm about to donate blood?

Fortunately, I can donate blood through the Red Cross, who still uses manual cuffs. If I go to another local blood donation organization, I'm turned away for high BP.

Has anyone else ever experienced this problem with automated BP machines?