Custom shop page with Woocommerce

I’ve had this issue before – https://kriesi.at/support/topic/custom-shop-page-with-woocommerce/
However, this time, I can’t seem to fix it. There’s something preventing my normal shop page from showing and the product archive 3-column product grid shows instead.
https://www.xavelec.co.uk/shop/
It seems to come and go.
Before, for some reason, I just needed to leave the shop page undefined in Woocommerce -> Settings -> Products -> Display. However, now, when I do that, I still get the Products Archive.
I’ve been able to “fix” this by specifying my “shop” page to be the Shop page in Woocommerce. The issue with that is the Avia builder is then disabled.
So can you please suggest what’s the best way of working around these issues? The undefined seemed to work but would sporadically go back to the Products Archive. Having to fiddle around with this constantly is a real pain. Setting it to my Shop page seems to work, but I have to change each time I want to modify the page via the Avia builder.