Yeah, this is something I have noticed as well, that I would attribute to google. I first noticed it on a site I use for tracking SEO rankranger.com I thought it was because of oh how they were using node. Then after we added Google Optimize to the google analytics module I noticed it on my dev site. What the issue is, is if you are using Google Optimize, they white the screen out and delay the showing of the screen.
This should only be happening if you are using Google Optimize and have an id entered. See here in the code, https://github.com/thirtybees/ganalytics/blob/master/views/templates/hook/analyticsjs.tpl#L26 That line is hiding the contents of the browser window, then this line, https://github.com/thirtybees/ganalytics/blob/master/views/templates/hook/analyticsjs.tpl#L29 is showing it 4 seconds later. You can edit the file and manually adjust the timer to less than 4000 milliseconds. The reason I used that value is because that is what the Google code uses. Here is a screenshot of what they give me in my account, notice the highlighted line, https://www.screencast.com/t/WkNFXg6h