erratic swimming

My baby Blue angel is demonstrating an erratic swimming. My cleaner shrimp used to be very aggressive in terms of picking the parasites off the blue angel. However, the shrimp stopped providing its service to the fish about a week ago. Yesterday, the shrimp passed away. I bought another clean shrimp and the shrimp just stay still, not moving at all.

I checked the NH3, NO2 & NO3, PH and SG. They all seem normal. I'm wondering what makes my shrimp inactive. Is there anything I can do to improve the situation?

thanks