Is myclonus jerks a commom symptom of fibromyalgia?

No. Fibromyalgia causes pain but does not affect the nerves that go to muscles. However, if you are taking a morphine like pain reliever for treatment of the fibromyalgia, this can cause myoclonic jerks. If this is the cause, it will go away if you decrease the dose of the pain medication.
Myoclonic jerks. Myoclonic jerks, especially at night, are fairly common events (as long as we're talking about just an occasional jerk) in normal people. They are not specifically a feature of fibromyalgia. The connection might be that fibromyalgia is associated with poor sleep quality, and the cumulative lack of sleep is likely to make myoclonic jerks happen more often in susceptible persons.