I recommend you use a rank tracker that doesn't track just your site, but tracks the top 20 sites for your keywords. If one site moves up or down, you can then see what's going on - ahrefs (new links or social signals) which can give you an idea of what you need to do to beat that site, or keep your ranking above it. Also, if someone is trying to take over your niche, you will know it when you see new sites popping into the top 20 for all your keywords.
XH