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Whenever I see a discrepancy, I always wonder, what are the differences in assumptions.

 

I never hesitated to use 33 Meg resistors for low f CMOS logic gates in my late '70's Aerospace days. For environmental protection, I added Silicone spray or more harsh environments like atmosphere reentry... GE RTV which even prevents exposed wires from getting melted or for RF ... tin-plated shields. They do make bigger resistors and Omega meters

"If probing the attached with say a scope probe, would you recommend a 100:1 probe?" 

-  Only if desperate. I'd only probe the lower impedance points to imply the performance, which is what I was thinking, by measuring the Vbe instead. But, I was lucky to have Tek FET probes where ever I worked, which requires critical care of any voltages or ESD E-fields> 25V.

Frank you are correct! Your simulation proves 2uA is insufficient with a 1:1 scope probe on the 22 Meg resistor.

So I examined our differences in assumptions to understand the disparity in simulations,

1. Was it differences saturation current, Is for the transistor?  I used 100 fA, The BC547A in LTspice is 4.679 E-14,  possibly

2. Was it hFE which drops rapidly with Ic < 5 uA and has a wide tolerance? Possibly, I used hFE =50  ( spec is 90 nom. at 10uA)

3. Was it the input pulse freq.?  LTspice used 100 Hz, I used > 5kHz  , Yes it makes a difference to the transistor .

4. Was it the probe test point? Yes, I assumed Vbe  as the critical test point,  as the 47k 100 pF  + probe attenuates the ripple and Rbe is a lower impedance at 2.6 uA

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