Brep union problem

Hello,

I have a problem i'm trying to tackle for another day and i can't seem to find a possible solution.

I have made an algorithm that generates me a diagrid mesh, which is composed from 4 lists of brep objects which are the beams. I wanted to do a solid union with all of them, but for some reason after i connect the fourth list suddenly SUnion returns that the incoming list of breps is empty, and when i check the exit of the fourth Extrude block (which gives me the fourth list of beams) it says its empty as well. The moment i disconnect the fourth list it goes back to normal.

I tried checking if i didn't disconnect or break something up to few operations before but everything seems ok. It's even weirder because i actually did the same thing few days before on the same algorithm and it worked flawlessly.

Could anyone help pointing out what might be wrong? I attached the file to the post.

Thanks in advance.