poly~ with a buffer~ for windowing generate crack

Hello, when I use my abstraction inside a [poly~ voice~ 16] I have some crack, artefact. Whereas when I use 4 of my abstraction in the same time I have no crack... ?

the main patch (to compare with and without poly~)

my abstraction voice~ for poly

it looks like the problem come from the reading of my window hann. because when I apply a window only with line (on the right part) there is no more crack.... Can many voices of a [poly~] object can read a same [buffer~] ?