There may be an explanation: Any filter has a break in period. I don't think your new filters were bad. Just not broken in.
I know it's probably overkill but I Zero filter all of the DW I use for making colloidal silver.
Suggestions:
1. Use that filter for filtering only water that has very low TDS to start with.
2. When "breaking in" a new filter run about 10 gal through it. I ran the same gallon through it 5 times & then switched to different DW a couple more times. I saved all that break in DW for use as rinse DW.
3. The ion exchange beads inside the Zero shouldn't really dry out so I keep a little filtered DW in the pitcher in between uses. (Do not use that storage DW for making colloidal gold or Colloidal Silver) I pour that into a container while using filter & then put it back in after use. Just enough to cover the bottom 1" of the filter.
4. If it has been a while in between filter use then I run about 1 Liter through it & that becomes rinse DW.
5. Freshly filtered DW seems to be best (for what ever reason). Don't filter up 5 gallons ahead of time & assume it will be the same weeks later.
MY cheap TDS meters read 000 for EVERY Gallon of DW I have ever checked. That does not mean they are all equal. I think there are TDS meters you can buy that go to 2 decimal points beyond what the cheap meters do (000.26 PPM TDS or whatever the REAL reading is).
BUT a meter like that probably costs $$$$.
There is another way you can check to see just how good a Gallon of 000 TDS DW really is. You can set up your colloidal silver cell & take a reading of how much current is flowing (with no EL, of course). It will be something like 0. 288 mA or whatever. (depends on the geometry of your cell & other factors)
A long time ago I checked 8 different brands of DW & I got readings that were 35% different, lowest to highest. All of these read 000 TDS on my cheap meters. So 000 does not mean there is nothing in the DW. All it means is that our meter does not have fine enough incrementation to read what's in there.
Tell Walmart that I will give them $10 for each of those defective filters you returned