Red Cherry Shrimp Questions

Having just returned from a 10 day holiday, I got home to find that one of my shrimp has disappeared. I'm not sure if it died, got accidentally sucked up the filter/gravel vacuum, jumped out, or *someone* got hungry...
 
On another note my Ambulia bunch had also vanished while I was away! It seems to have died off and all that was left was some measly stalks. I suppose it's possible the dying plant caused an ammonia spike and the shrimp died from that?
 
The one that have vanished seemed smaller than the other five and never coloured up (in fact it turned clear). I've also noticed that two still alive aren't really eating when I feed them, and the others aren't as active as normal. This has just happened in the last two days (since adding a new plant). I checked the water levels yesterday and all was OK. 
 
A quick background on my tank:
30L glass aquarium, heated, filtered, gravel substrate, planted with hygrophila, bacopa, 2 crypts, java moss and now lace fern, weekly 25% water changes using Seachem Prime, test water every 3-4 days using API Master Test Kit, feed betta twice daily, feed shrimp once every two days (flakes and bloodworms), dose a tiny drop of Flourish once per week.
 
Anyway I have a few questions:
 
1. Is it normal to for shrimp to disappear? 
2. Does molting also slow them down?
3. Is it possible to add new water too quickly to the tank?
4. Am I doing anything wrong?
 
Sorry for the long message, I'm just super keen to do the best for my critters!
 

 

1) Yes it is. Back in September, I moved my cherry shrimp from the small tank to the big tank. I have been finding and moving others ever since, the last ones (yes, 4 of them) just this last weekend. Some of them clearly hatched since September. They will hide wherever they can.
 
2) Molting makes them hide more, they need to allow the replacement skin time to harden up, so they hide away wherever they can. Not sure what you mean about whether it slows them down.
 
3) In terms of it affecting the shrimp, then I've never found a problem with the way I replace the water, which is directly from a bucket, but then I take a good minute or so to add the bucket. I don't want the water flow re-scaping my substrate for me!
 
4) You don't want to be feeding the betta twice daily, once a day is fine, and if you miss a day every now and then, no-one's going to complain. Remember that the betta will also eat the shrimp food, and vice versa.

Thanks for your reply. By slow down I meant become less active, sorry for any confusion.

You're lucky mr. betta doesn't attack them continuously like mine did when I introduced them! They have plenty of hiding in my 40L, though. Bought 2 have 2! lol It's a good idea to quarantine plants like new fish. I've read even on here when someone added new plants a shrimp got sick. The plants could have had pesticides or metals from the source that shrimp especially are weak to. A nice rinse in a waste water bucket isn't a bad idea before introducing the new plant if you want to skip quarantine.