sudden drop in conversions, no change of traffic.
At a basic level there's really only 2 core elements that could be at play:
1. an onsite issue(s)
2. an issue(s) with the traffic coming to the site
Onsite issues are a plenty:
- site speed, known to affect conversion rates. Yes, we all check our sites for speed, they are lightning fast, but really we never know exactly what the end user is experiencing. Many things can have an affect on our site speed that we may never see. One that comes to mind is ISP throttling. Security certs, addons/plugins, third party analytics - all can have issues periodically that we may never see.
- server issues
- merchant account issues
Incoming traffic issues.
The google serps are so incredible fluid these days, they change constantly. Ads move, widgets come and go and morph, constantly, minute by minute, search by search. All this movement can cause constant changes in the person clicking thru to a site. Minor changes in position can make a huge difference in the searcher's buying cycle. We have seen this in our testing in adwords, the top position gets a ton of non-converting traffic where maybe the second or third position gets slightly less traffic but better converting traffic. Same holds true for the organic results, move up a couple of spots and the visitor dynamic changes, a lot in most cases.
It might be that we don't see these patterns from Bing/Yahoo traffic because their search results are not as fluid as google's.