Old cleaning shrimp - health problems

I had a pair of adult Lysmata amboinensis for more than
a year now. Couple months ago one of them disappeared from
the tank in unknown circumstances... Probalby has been eaten
without leaving any traces of body remains...
Sept 24th the second from the pair released larvae as usual
but did not molt the next morning. Actualy, it did not molt
at all. Last time I checked it still has no new eggs.
I am little bit worried because after the last molt it
has curly antennas for the first time in its life...

The water condition is good, the other shrimps are molting
with no problems, no curly antennas, etc. Hermit crabs are
doing fine too so I do not suspect problems with minerals
(like iodine, etc).

What could be the reason for that? Do shrimp age? What is
their average lifespan? How would you recognize old shrimp?