@BUMPandHUSTLE I’ve been struggling with trying to solve this issue for about 3 hours, thank you so much for posting your solution. I also had the Google Optimize integration enabled, and sure enough, I was having the same issue.
I can confirm that there is definitely a weird delay between loading and the first paint on my site as well (without optimize), but haven’t figured out what it is either. Without optimize it’s a super short delay though, so I can live with it.
I tested the anti-flicker code from Google Devs, and it greatly increased the load time and the delay until first paint on my site.
Thanks again for figuring out it was Optimize, I was about ready to give up.