(Again) So far so good.Thanks for your help Moritz. As you can tell, I’ve sent a lot of time on this!
Increasing the session lifetime seems to have worked.
I still don’t see why it was causing the £0.00 / 0 though? When it recreated the session it gave it the same ID and the products where still there but weren’t displayed until a cart action was made.
Presumably this is a bug?