I put 10 Amano shrimp in my 45 gal. I only ever see 3 or 4 at a time.
I only have tetras, so I know they weren't eaten and I have a good
filter intake so I know they weren't sucked up. I never had a problem
with them escaping, but I have heard that they can do this mostly if
there is a problem with the water quality.

5 shrimp in a 90 gallon will vanish, and they won't do much if you get
a real algae outbreak. THey are not nocturnal. Angelfish will not eat
Amanos...they are too big for them.