Excel 2013 results non-zero going to zero

I'm working on a fairly complicated spreadsheet and am debugging various formulas.
Often I've seen this happen:
A cell which should not be zero, is showing zero.
When I run Evaluate Formula, it all works as expected and ends with a numerical value as expected and intended.  Then the final evaluation of the numerical value ends with a zero value in the cell.

What's going on here?

Here is one of the formulas:
=+IF(   AND(AX109<>0,     OR(    AND(O$15, P$15, AI110=0, AI109<>0, AO110=0,AO109<>0),    AND(O$11, P$11,NOT(AND(O$15,P$15)),  AI110=0,AI109<>0),    AND(O$13,  P$13,NOT(AND(O$15,P$15)),  AO110=0,AO109<>0),    AND(O$33,P$33,IF(O$34*BO109>BP109,TRUE,FALSE)), AND(O$18,P$18,Y110=0,Y109<>0),AND(O$24,P$24,AC110=0,AC109<>0),AND(O$31,P$31,AD110=0))),AX109,0)

In this case, the last term is operative:
AND(O$31,P$31,AD110=0))),AX109,0)

AND(O$31,P$31,AD110=0) is TRUE (all the other terms in the OR are FALSE)
So, in the result, we should see the value from AX109
And, indeed, the value in AX109 shows up in Evaluate Formula
The Evaluate Formula ends up with IF(TRUE,AX109,0) and next shows the value of AX109 only as a number and then when pressing Evaluate again, goes to zero.
The result in the cell is zero.