It is late and I am not thinking to clearly but I have a theory.
I am theorizing that your FC is higher than 10 ppm and you may have to add even more R-0870 to get a valid reading. If you have an OTO chlorine test (the one that gives shades of yellow for total chlorine) could you use it and tell us what the color is?
From the extended test kit directions on OTO chlorine testing:
You can use this test to get a vague idea of extremely high TC levels. If the sample turns a particularly vivid yellow the TC level is between 5 and 15, light orange is between 10 and 20, dark orange is between 15 and 30, and brown is 30 or higher.
If your's is dark orange to brown then your FC is pretty high and you do probably need to add more of the R-0870.
If the FC is high then this could also explain your strange ph result. First, when FC is over 10 ppm the ph test is not valid. In addition, my understanding is that at high FC levels starting somewhere between 18 and 23 ppm for the Taylor chemistry the phenol-red indicator dye used for the ph test gets transformed into chlorphenol-red indicator which measures PH between 5.2 and 6.6. Some people have reported a purple color when this occurs.
Again, I am tired, but I think this could be the problem you are seeing.
How much chlorine were you adding?