A few things I noticed/thought I should mention, in no particular order or level of importance (keep in mind I didn't get nearly enough sleep and haven't really for the last 16 months, so I'm bound to be off kilter, but I figured I should put them up since I did ASK what was wrong!)
Red Cherries are typically very flexible (as shrimps go) and have a decently wide range that they can do well with. But it's likely better to aim for the middle of a range if you're going to fiddle with things. Your 300+ TDS, while quite surviveable, seems on the high end of things (most people aim for 200ish), especially since your tap water is low and you have to use a remineralizer - I would use a tad less, save some money.
As has been mentioned by many people/sources, it's probably at least as important to maintain fairly constant parameters as to aim for "ideal" numbers.
Do you actually see dead shrimp? In a decently planted/decorated tank, sometimes "disappear" could just mean they're hiding better than you think. I had a few distinctive (easy to recognize) shrimp that just spent a LOT of time out of sight - sometimes it'll be 2 weeks before I spot them again. The berried females are especially prone to hiding. Hiding may account for a few of your missing shrimp.
Do you ever see any odd things on or about your dead shrimp? (possible indicators for cause of death)
How do you keep the water temp at 73 in Reno?? (assuming Nevada) I'd have though it'd be a lot warmer than that for at least 4 months of the year. Sorry, not quite shrimp related... just a random thought. Although... the outside weather/season could affect your shrimps' breeding. I've had long-time shrimp keepers tell me their shrimp won't breed for them during _X_ season (the low seasons varies).
Things that could affect breeding:
I used to be lazy about water changes, but now I think they are great!! You don't need to do huge ones - for the sake of convenience (size of my aquarium dedicated bucket), I usually do about 15-20% once a week. BUT. I purposely use cold water for my change and uhh... tend to dump it in relatively quickly - a minute or 2 for the small tanks. I AIM to drop the water temp by about 2 degrees. This tends to result in a bunch of newly berried females the next day. (Possibly the drop in temp --> new rains -->fresh food supply -->time to breed idea).
The other thing that may help speed up your breeding slightly is to increase your tanks' temperature slightly 75-6 ish (higher temps = faster life cycle; this won't do much for deaths though).
More plants are always good for breeding too - more surface area, more biofilm for the babies to eat - especially if you have places that only the smaller ones fit. I have a bit of moss wall on the back of all of my shrimp tanks. I usually stuff a couple of the IAL leaves or other dried leaves back there with most of it sticking out - the mesh helps hold them in place so they're not too cluttery, but it also creates baby-only zones on the leaves. And when I say a couple, I mean my 10 gallon usually has +3 leaves, added 1 per week or so - that way they have a chance to soften and grow stuff before the older ones are all gone. If you're REALLY trying to breed more and have the time/equipment, you can try setting up a maternity/nursery tank. Mine are just external breeder boxes attached to the main tank, so no extra tanks to handle (other than the occasional thorough clean they get when between batches). I find that my baby survival rate is anywhere from 50% to +300% higher in breeding boxes. Perhaps because they never have to compete with adults for food. My most recent experience with this - I'd put my berried TB females in their own box, at first because I wanted to keep track of the babies' growth. But they've been spitting out about 3x the number of month old juveniles per female than the supposedly more prolific CRS. It can't be water parameters etc... they all share the same water. So now I think I'm doomed to have breeding boxes hanging off of various tanks ?.
You may have gotten a batch of inbred shrimp that carried some less than ideal genes and they're slowly showing themselves in a constant low stream of deaths. Because it's next to impossible to tell if that is or will be an issue (unless you happen to have a spare equipped Biology lab and some minions to do the work for you), I generally try to get livestock (be it fish, shrimp, insects, whatever) from multiple sources. I'd rather go to the trouble of driving to 3-4 locations than wonder if they're struggling with lethal recessives in there.
Fiddling with the water parameters will often stall their breeding, so you may have to give them time to get back into the swing of things.
Hopefully something in there gives you some ideas that help. And maybe someone with more experience/more awake will chime in!