My Marineland 5g hex does that every time I do a
water change and forget to unplug the filter. Once I loose the siphon I have a "somewhat" hard time getting it going again. Last month I had to take the filter into the kitchen sink, take it apart, clean it and start over. It has always worked after a few scary moments. As a matter of fact there is a web site that sell parts for it. I almost bought one, but like I said, it started again so I dropped the idea. I still think it might be a good idea to order a spare just in case.
Good Luck