Hi!
This is really strange.
I tested in Version 2.73.1+171220 and found no issue.
My condition is: sum(R1,R2)!
Here you see:
The question is displayed because the sum is equal 4
But here the sum is equal 3 and the question is not displayed.
No difference if I display "question by question" or "group by group".
Unfortunately I cannot test in your - older - version.
You should send an lss export of the survey only containing the affected questions.
Joffm