Certain Products suddenly not showing in Front Shop?

[AZC]

Hi Everyone,

 

I am using prestashop 1.5.3.1 (yes yes its an older version but cant update at present)

 

I realised that some of my products have suddenly stopped showing in the shop?

 

They are all enabled in the back office and were working until about a week ago.

 

I have found that accessing and re-saving each product causes them to reappear in the front shop?

 

Does anyone know why this would happen and how I can solve this without going to each product separately.

 

Thanks