Google has announced that beginning immediately they will be “encrypting all communications between end users, websites, and their servers” [direct from Google].
Basically, this means that you may see a change in your traffic numbers as a result of this change. According to Google, traffic that is encrypted with HTTPS can be slower which may have a negative impact on the user experience, possibly causing the user to close the browser quicker. As an example, a visit that ends in less than 1 second will no longer be counted. This could result in a lower than normal bounce rate [Google’s definition of a bounce] because this action could have been counted as a bounce in the past.
Another contributor to a lower traffic count could be firewalls. Some firewalls are set-up to not send encrypted data. If a user is accessing your website from behind a firewall that prohibits the transmission of encrypted or https data then they will no longer be counted within your GA data.
The best thing that you can do is to monitor your GA data and see if your site is being affected. If it is, look for ways that you can speed up the load time of your page. As an example, try to optimize any bloated code, or reduce the sizes of any image, videos, or other bulky items on your pages.
There isn’t anything that can be done about the slowdown caused by the HTTPS, but you can look for other areas to reduce the page load times, across your site.