Non pro. Took a look at the manual, and here are some comments... probably not useful.
Dropping to 3 grains from 20 is not so good in my opinion. Is that sample from cold water, or from hot which might have sat in the tank for a while after you added the softener? I test 1 or less on harder water than you on what seems like a very old softener.
I think you are setting this to regen every 7 days, or sooner if you have a lot of use. There are diagnostics like HR Hours in Service since the last regeneration cycle. VU is volume used since last regen. I presume that is gallons, but their example of 25,000 seems very high.
Are you sampling the day after a regen, or the day before a regen,.
Is about 7 pounds of salt disappearing from the brine tank each regen? I bring that up in case you have a salt bridge or some other thing limiting the brine flow.