6:1 bad to good ?
sounds as if either the good water is actually the bad water, and vice versa .......
Or
A seal is not sealing well, and allowing tapwater to leak by the RO portion ...
Or
The RO membrane itself has a pinhole or rupture, that is allowing leak by
Could be one of those ( or not ) ???
If you don't have a TDS meter, you could run an alkalinity test on the good and bad water wes.
The RO/DI should turn color immediately when you add the first drop of reagent ( in other words .. the good water should have a very very low alkalinty )