@highlysceptical You are welcome here!
FIRST:
Google Search Console says there is 1 security issue but does not say what it is...
The certificate being served doesn't match the expected hostname.
Expected APEX hostname: = acousticdesign.co.uk
www.acousticdesign.co.uk and api.acousticdesign.co.uk are covered by your certificate but NOT your apex domain name.
You could "expand" your certificate to include your apex domain to resolve that part of the issue. (might also help with the branding placed on your site but frankly I dont really know for sure)
SECONDLY:
It is interesting how "big tech" is acting these days. And to no fault of your own I suppose (Mostly). I suspect the "classification" or "branding" you have been awarded may have something to do with the "first visit" pop up script in your top page.
Result from quick scan:
You can attempt to get reclassified here:
https://safebrowsing.google.com/safebrowsing/report_error/?hl=en
Hope this helps.