if you only hedge (or better say make neutral position) by selling the Future for the same stock / bond (that means all factors affecting the price movement are same and assuming the there is no mispricing in the futures, you will earn risk free rate as future price will converge to spot price as you near expiration.
However, since we are hedging using different durations, it is safe to assume the ‘asset in portfolio’ that you want to hedge and the underlying asset for the future will have different sensitivity to change in rates, which could be due to duration, convexity, or quality / spread or general market mispricing (not all investment grade bonds have exactly same spread). Given this, it is good to assume imperfect correlation between the asset and the future, which is the reason for basis risk.
To summarize, if you can hedge your position with a perfectly correlated future or underlying, there is no basis risk.
for yield beta - it is a measure of the sensitivity of a bond’s yield to a general measure of bond yields in the market that is used to refine the hedge ratio (source: likeforex.com)