Bones lost its animation despite it has a curve

I found few people complaining about animation that does not working properly because some bones lost animation despite the curve editor shows valid curves and red underlined name of bone instead of type of curve(Quaternion etc.).
I have found only one solution. To click channel and then on revive F-curves… But works only for last selected bone. At first it appeard on only bones that were made by extruding miirored by x axis. Few attemps later( new clean armature with copied curves.) random bones started to forgot to move.
I feel sorry for my fish that looks like crippled (Here). I would be very happy if you even try to help her. The most welcome would be solution but even a hint or description why did it occur would help.
Thank you