You can manually add any sites that don't work as 'always allow' in eero secure.

HOWEVER the problem is you have to know what the sites are. If it's a simple case of an initial page not loading it's easy. If it's an embedded device / not with browser, or perhaps a piece of critical function on the page, then it's a lot harder.

Though eero secure generally works well, this specific limitation - not knowing what is blocked - makes it too tricky to mitigate, so we've found it easier to use another service that offers dns filtering/blocking instead (no kids, more for our own preferences), since we can see logs of any blocks or run a trace and easily see what we might want to add - even via a single click). 

This is the big issue I see with eero secure.