How old is child again?
If child is younger than HS, call the coaches and music directors and ask for schedule and ask what happens in they miss one or two days. I'm sure other kids miss every so often. Also, you/other family member can go see child then take child from a Fri or Sat event. If it is a Sunday event, have child come to you, bring child to event, and have child go home early after event (or bring child out to eat and bring child home after).
If child is in HS- same as above but usually can not miss if it is a school class (band) It may affect grade but talk to teacher.
If there is a time you will miss, do not tell child/mother until child gets to you that weekend. Explain to the child, sometimes we have to make a choice and this weekend the family is doing xyz. I talked to your teacher and all is good. Then text mother "child will not be at xx this weekend, we have other family plans, talked to teacher about absence" Then ignore and return messages, shut off phone.
Pick and choose your battles, especially if you are at work part of the weekend. Will mom fight other family members to go and pick up or return child? If so, you may need to change
court order to "Dad may send a friend/family member for pick-ups/drop offs".
Good luck!