So I have transferred to a new host to resolve this issue - their response below. Also there is no download available for the latest version of the theme and I am still in support period.
From my New host – can you please send me a link to download latest version of the theme.
YITH WooCommerce Compare (in fact, it was the Boutique theme failing in trying to call a function in this plugin)
Boutique Toolkit (a companion plugin for the theme)
I have had to disable both these plugins so that I can take a full backup of the site.
Please note, I also had to disable JetPack.
I will not be able to resolve all the issues you have been experiencing until we get the latest version of the Boutique theme and it's companion plugin -- any luck getting hold of those?