One more question: What were the filtration settings, if any, when doing the contact sheet or was it simply white light and did anything change when doing the test strips? I just cannot work out what had changed to produce a neutral print at f16 and 7 secs and a cast at f11 and 3.5 secs.

The only changes I can see is that the contact sheet was one sheet, the perfect print test sheet was another sheet and the same exposure print on which the cast re-appeared was a third. So bad sheet, good sheet, bad sheet???? Makes no sense

We need this OP to read our posts and respond. We can speculate until the cows come home otherwise