AAAARGHHHHH, this just gets more weird.
I’m able to replicate the flickering issue locally by activating my child theme, as soon as I switch to the parent theme the flickering completely goes away. I also managed locally to pin down the issue to being my child styles, because if I remove all my CSS from my childs stylesheet this also stops the flickering.
However, if I either switch to parent theme or delete my CSS from the child stylesheet on the preview URL it has no effect and I still get the flickering issue, even after doing a hard refresh!. I’m not using any cacheing plugins either.
It doesnt make any sense!! 🙁