A lot of change in a week or so. Hard to know if this is related to the GP updates or WP 6.1 or something else unfortunately. Oembeds for posts and websites are behaving badly since the updates. See the link to Acton Aroboretum at the bottom of this post: https://stoneyard.com/acton-arboretum-natural-stone-bench/
It is showing the link then the home title then what looks like an iframe of the page but the hamburger menu in the iframe doesn’t work.
Even adding a URL for a local WP post which used to very nicely show the post via oembed now tries to iframe the whole local site in a similar way.
I’m going to go try turning off various plugins on a staging copy to see if I can isolate the cause. In the meantime, have you heard of this on any other customer sites?