Hello @Han_Lauw,
Are you using the latest Poly firmware (at minimum version 2.04)? There was an issue with poly a while back which was resolved via a firmware update on the GoFigure app:
Also, as others have mentioned, we have often seen sub-par performance from Apple networking gear, so this might also be the cause of the issues.
If you have another router around you might want to give that a try instead.