Manage to get around it by applying the modifier in edit mode, and then switch back to sharp instead.

I have the same problem that Unity crashes while trying to apply a Remesh modifier to a fairly complex mesh. But the problem occured first after trying to crank up the regular Octree Depth to around 9 and then changed to Voxel to see what it was. And now the default value is set to voxels with 0.1m voxel size that craches the program very time.