Assuming that the cause of the error lies between the keyboard and chair I cleaned up (rewrote) my code. What I discovered was that a list (of lists) was causing a memory problem.
aListOfData = RandomInteger[10, {10000, 4}];
(this mimics my data set) followed by
howManyRandoms = 1 000 000;
aFixedListofRandoms = Table[RandomChoice[aListOfData, 220], {howManyRandoms}];
This list, the purpose of which is to allow the Monte Carlo sim to run against a fixed list, causes the allocated memory of the Wolfram Kernel to increase hugely each run of the assignment On a 2012 MacBook Pro with 16 GB running 10.14.6, running Mathematica 12 I have seen the following memory jumps (each row is a restart of Mathematica):
164 MB, 7GB, 13GB, 20GB, 30GB
164 MB,7GB, 27GB
These memory increase are not surprising considering the size of the table being created. I also ran a trial version of Mathematica on a windows computer with similar memory increases.
Even when the memory in use was a'mere' 6GB I begin to notice a slow down of cell calculation and general responsiveness of Mathematica, and of course the 'dynamic evaluation' error. The original value of 'howManyRandoms' was 100; I used 1 000 000 elsewhere in my coe and obviously set this one incorrectly without realizing - thus falling under the heading of "un-aware" & "all the time" . Returning this back to 100 allows Parallezie to function again.
Whether or not 'aFixedListofRandoms' is used in further calculations (i.e the Monte Carlo simulation) with a 'size' of 100 or 1 000 000 is irrelevant to the slow down of Parallize. As long as the huge table was created somewhere (and therefore assign to some Out[]), there is the slow down .
So thanks for looking into this. I have learned some more about Mathematica, which is always good.