Ok, actually makes perfect sense the babies survived. The adults may not have been able to handle the parameters you had them in, could have been very different from their original breeder and slowly over time, it has killed them. But the babies were BORN into your parameters and have adapted. That's why they survived. If it was a water quality issue they would not have (as in something toxic, ammonia, nitrite, etc, etc...not talking about pH, Gh, KH here). I have actually gone through this myself losing adult shrimp on a weekly basis but babies born into the tank alive and doing well.
As far as going from saddle to no saddle and no eggs, this could be a few things. #1, it's not uncommon for first time mothers to drop their eggs within hours or days of being berried. Also, you could have sterile male shrimp in there. And I had the problem with no shrimp berrying when I was stressing my shrimp out with too frequent water changes (which included vacuuming substrate...newbie mistake and I don't touch substrate now). So there could be a lot of reasons but those would be my first guesses. Give them time, they'll get the hang of it.
Also, one algae wafer a day isn't the best idea. Algae wafers can be high in protein which may (or may not) cause molting issues down the road. Secondly, a variety in the diet is important. Blanched spinach, kale, zucchini, fresh veggies are good for them and they'll love you for it. And lastly, feeding once a day especially if it's a whole algae wafer is overfeeding. When I feed processed foods I feed very small amounts, like a piece this big __ for 20 shrimps or so and every other day. Now, I have a CRS tank I only feed twice a week. On the flipside I have a tibee tank I feed 5 days a week but it's due to the aggressive nature of the particular shrimp I have in there. Keeps the aggression down.