While the most common reason for lost keyword rankings is algorithm updates, there are a few other possibilities for why this could happen. One possible solution is that your website has some technical issues, such as your site being down or your server having limited availability. These problems often can impact your rankings, but they usually turn around relatively quickly.
Traffic drop can also be due to seasonality. If your industry is seasonal or particularly volatile and/or trendy, then this could also have something to do with it. Another potential issue could be your analytics platform, as they have been known to be glitchy from time to time and give incorrect keyword and traffic information. But at the end of the day, if you have seen a significant decrease in traffic, and it has lasted for longer than a few days, it’s most likely because of an algorithm update or Google penalty.