'Suddenly loosing' the upstream channels sounds like you got throttled by your ISP.
'Suddenly losing' the upstream channels sounds more like a line or modem problem (or possibly just some local CMTS maintenance). Upstream or downstream channel bonding is negotiated between a DOCSIS 3 modem and the CMTS. There is no way I know of for that to be done on a per customer basis. Besides, Comcast has much more sophisticated methods of throttling should they choose to do so again. -- We can never have enough of nature. We need to witness our own limits transgressed, and some life pasturing freely where we never wander.