I have had several times either just been invited to evening for weddings when my parents were invited to the ceremony and both afternoon and evening and on a couple of occasions have not been invited at all to cousins weddings.
As my dad was one of ten, there are quite a few cousins that I have had little contact with since we were children, so tbh, didn't expect an invite!
In this day and age, with the costs of weddings, hard decisions have had to be made and especially at the moment when restrictions have been made about the number of people that can be invited.
Maybe it's a case that the aunts and uncles were on the invitation list and when the restrictions were relaxed, it meant that the cousins could be invited to the evening function that previously would not have happened!
Above all, it is the couples wedding so sorry, but up to them where when and who their guests are is up to them.