Ok,
I heard back from my hosting company – this is what they said
“That error specifically isn’t our end but is based on whatever your site is hosting that Google Chrome is picking up on. If we disable rules via Modsec this still won’t stop any issues from the browser itself”
This gave me a clue, my main server has ssl so my development sites are in a sub folder and ssl was not set in wordpress settings, so this was throwing up the errors
Many thanks – great plugin