because a widely reported GA issue was recently a source of annoyance. See the discussion here: [webmasterworld.com...]
It is unlikely that the bug discussed in the thread would be directly related to this issue. That directly impacted traffic.
But if we are talking about GA, and potentially other similar tools, then you should check the traffic source to see if you are being impacted by referral spam. This is where a bot makes calls directly to the GA endpoint using your tracking code, thus recording hits to your website when none actually occur. This almost always results in 100% bounce rate for those hits. These hits can be many, typically in a very short span of time, eg: hundreds in 1 minute. Note your server never sees this traffic, so the server load is not impacted. If the many "fake" hits results in a large number relative to your normal traffic, then it can cause aberrations in your stats like the sudden increase in bounce rate.
This "fake" traffic can easily be filtered from GA. The traffic can't be blocked, because it never goes to your server so there is nothing to block.
Similarly, the same impact can be felt if a bot is actually navigating to your website and going to the same pages with a new session for each request. In that case, filtering GA will not help. You will need to find the culprit in your logs and block it.
Finally, it is possible that Google made change that impacted the type of user that your site is ranking for, and getting the intent of these "new" users wrong. This scenario seems the least likely to me, but other will say it is the most likely. I would first investigate the bot traffic, and eliminate that as explanation before speculating about changes in the Google SERPs.
The above presupposes that you have not made any changes to your website. Sometimes even small purely aesthetic changes can cause js to fire events (or not) that will impact bounce rate.
