My Ph swings from 7.5 to 6.4 almost every day but I only have 3 cherries in a fish / planted tank with pressurized CO2 & my shrimp are doing really well. Although I am not sure if they are too old to breed. I have been told that 2 or 3 shrimp in a heavy planted tank are not going to breed. I also read that that the stripe down the middle actually means the shrimp are getting older NOT dying. My RCS shrimp have had a stripe down the middle now for 5 months & they are still doing well. If they died in the next few months I doubt it was because the stripe appeared but more because they died of old age. The stripe means they are old shrimp. Young cherry reds do not get the stripe until they are at least a year old or more.
If my shrimp were more plentiful & younger they probably would have breed by now. I doubt the ph swings are really that bad because in nature the ph swings a lot. It is probably a myth the ph thing. If your shrimp are breeding with a steady ph than it is probably because all else is good.
1 last thing. I do not always consider breeding the only indication that a species is doing well. All it takes is 1 thing that can turn the corner for breeding but the species can still be doing well. My 2 cents