Just quickly wanted to put my discovery up here. After years of headache and having found no other artist who was able to tell me how to fix this, I just hit the solution.

When you got modular on grid meshes in Max/Maya, and you bend them 90/180/270 degrees, their ends are never ever on grid, even though the original mesh was perfectly on grid. Most people, that included me, would in that case manually move the vertices on one end and snap them to the grid. That gets very tedious to do very fast though.

I just found out that if you take the length of the mesh, divided by exactly 86.0576519035213, and then take the result of that division and use that to offset the center of the bend deform with into the opposite direction the mesh bends, then the end of that mesh will be exactly on grid! So for example, a 1024 long mesh that bends needs to have its bend pivot point offset by 11.899 units and it will end up exactly on the grid.

I verified this on all kinds of Unreal grid sizes. No idea how it holds up on other scales.