Splitting and joining brep fail

Hello,

i want to split a brep by a surface with brep split buti got the error message "split did not succeed".

Days ago i did the same in an earlier version of the definition and it worked.

Another thing is that i want to join 2 breps , i got no error message but i didnt worked, there are still to many elements.I think it is maybe it is because one of the breps is inclined. but they fisically touch.

Can anybody help me?

Thanks in advance!