Hmm, this definitely used to be an issue when the site first switched over, see, Why do my 
Saved Items keep disappearing?, I never had the issue and I thought it had been fixed. Maybe one for @Lovehoney_Brenna to query the LH tech team on again? Unless our own forum tech genius @Ian_Chimp has any possible insights?
Just to check, I’m assuming you’re signed in to your account when you add items to the saved list and when you’re checking it? The site does have a habit of logging us out unexpectedly.