The various chemical reactions listed for the interaction of sodium chlorite and acid are usually looking at producing small quantities of low concentration chlorine dioxide. When you use high concentration chemicals and larger quantities you then have to look at the thermal part of the reactions. The conversion of sodium chlorite to chlorine dioxide is exothermic. If this process begins to locally boil the water, you end up with extra chemicals in the mixture. Part of the extra by products produced is chlorine.
When testing chlorine dioxide for water purification the production of THM's was of great interest. It is known that THM's are produced as a by product of chlorination, but it wasn't known if they were also produced using chlorine dioxide to disinfect the water.
Producing chlorine dioxide for chlorine sensitive testing required a little different approach. The purist chlorine dioxide was produced with lower concentration sodium chlorite (around 2.5%) and limiting the chlorine dioxide solution to 1000 PPM or lower. In addition a scrubber was added to the process to remove any chlorine produced. Also, only a small amount of acid is added at a time and then the reaction is allowed to go for 5 - 10 minutes before adding more acid. This greatly limits the exothermic effects of the reaction. The chlorine dioxide is transferred by gently blowing air through the system.
As you can see, this is a very controlled process that is far different from Jim Humbles method of mixing the acid and sodium chlorite together then heating the mixture up to drive off the chlorine dioxide.
The industrial applications that use high concentrations of chlorine dioxide have noticed this and take steps to either eliminate chlorine from forming, removing the chlorine from the solution before use, or cleaning up the chlorination by products at the other end of the process.
I don't know how much chlorine is produced with the various methods of producing CDS, but it seems to be enough to change the pH of the water. It is much lower than the amount of chlorine exposure from Miracle-Mineral-Supplement 2.
I mix up a chlorine dioxide in water solution when I need it. This eliminates needing to store high concentration solutions and any worry about how stable those solutions are. I use 5% sodium chlorite, 6% HCl, and then buffer the solution to a neutral pH.