A cable that short shouldn't be a problem, so long as it's certified "high speed".
What are you usually watching when you have a dropout?
Cable TV decoder boxes often have problems. Most have digital audio connections in addition to HDMI. The usual workaound is to connect the HDMI cable directly to the TV and use the digital audio connection to connect to the receiver. Alternatively, try to get its firmware upgraded or have it replaced by a better model.