I have a similar issue. On browser page load my site title looks like <title>SiteTitle | SEO Title | SiteTitle <title> The site title is repeated.
Then refresh the browser and it then looks like:
<title>SEO Title | SiteTitle <title> which is what I want.
If I leave that page and return to the exact same page, the same thing happens: refresh the page and all is good again.
This looks like a cache issue but no caches are enabled. I've used Yoast SEO on many sites but this is the first time I came across this issue. Until pages get indexed, I'm not sure what Google actually sees.
I'd welcome any ideas anyone? Many thanks.