A few thoughts:
1. The best way to find out is to do a survey of your existing visitors/subscribers. Period. There are various tools that allow you to do it for free. Even if just a handful of people complete it, you will still be able to see if there are any items that commonly pop up.
2. If you changed anything in your page content or layout, you may want to use HotJar insights - a tool that analyzes visitor usage of your pages, and tells you where you are losing visitors.
3. Did you change anything in your site/blog recently? if you did, did it perhaps slow your site/blog down? That could cost you. Maybe you activated an additional plugin or two, or substituted one for another - and the way the new plugin(s) work slows the site down. Or maybe you added a new theme/template/header image/slider...
Any of those could be the culprit.
Once again, if you suspect that might be the case, there are various free tools that will let you check your website/blog speed online, and even show you exactly what causes it to be slow.