Talk.
(I was so tempted to end my answer at just that one word.)
Seriously, though - your problem is that you don't have a single, cross-functional Team. You have four teams that call themselves/are called one team.
Your developers (and they are all called 'developers' in Scrum parlance) don't need to be generalists, but the goal is still for them to become T-shaped. The only way for them to do this is by associating with each other, talking about each others' specialties, learning, and assisting one another.
As long as your 'designer' developers look at a 3D art task and think 'that has nothing to do with me', this problem is going to persist.
What you need to do is change 'that has nothing to do with me' to 'that has something to do with my Team. I wonder how I can help?'.
The first step on that is getting your Team to consider itself a single coherent unit, rather than 4 connected sub-teams.
Get them talking to each other.
Within a Scrum Team, there are no sub-teams or hierarchies. It is a cohesive unit of professionals focused on one objective at a time, the Product Goal.