UPDATE: I replaced the flush valve / flow restrictor inside the Smart Buddie, and the system is now behaving much more consistently.
After the replacement, the pressure is holding steady at around 80 psi, and the product to waste ratio is now approximately 1:1.15. The rejection rate is about 94%. It’s not perfect, but it’s an improvement, as I was getting around 90% before. I may try a higher quality membrane in the future, but for now, if it remains consistently at 94%, I’m comfortable with it.
It has only been about a day since the part was replaced, so I will continue to monitor the system over the next few days to make sure everything stays consistent.