After a series of wipes and re-installs, decided to install the recommended modules suggested by composer and although not all of those could install, with the ones that did the shop seems far more stable (so far). Also updated to the latest version of guzzle - this may have helped as well.
The modules recommended (not required but perhaps some of them should be) are:
symfony/event-dispatcher suggests installing symfony/dependency-injection ()
symfony/event-dispatcher suggests installing symfony/http-kernel ()
burnbright/silverstripe-shop suggests installing burnbright/silverstripe-shop-comparison (Allow comparing products side-by-side,and introduces a model for detailed specifications.)
burnbright/silverstripe-shop suggests installing burnbright/silverstripe-shop-coloredvariations (Select colours for variations)
burnbright/silverstripe-shop suggests installing burnbright/silverstripe-shop-shipping (Provide various shipping methods.)
burnbright/silverstripe-shop suggests installing burnbright/silverstripe-shop-geocoding (Geocoding support for addresses and visitors.)
burnbright/silverstripe-shop suggests installing burnbright/silverstripe-shop-discount (Create coupons and generic discounts to be applied at check out.)
burnbright/silverstripe-shop suggests installing burnbright/silverstripe-shop-googleanalytics (Records shop sales sales in google analytics.)
burnbright/silverstripe-shop suggests installing tractorcow/silverstripe-opengraph (Implementation of the Facebook Opengraph protocol for Silverstripe)
burnbright/silverstripe-shop suggests installing markguinn/silverstripe-shop-ajax (Basic ajax behaviours for add to cart, etc)