Royal Mail Delivered But Not Delivered

Has anyone else seen an increase recently in Royal Mail marking items as delivered but the delivery does not actually take place until a few days later.

This is always RM48 items and the items can normally be fitted through a letter box.

It is really annoying as the customer is annoyed and we push back as the item is marked as delivered.

I have had a few like this over the last month. I don't think it is the customers lying as we have had a fair few all different parts of the country.

Is it something RM are doing to make their delivery rates look good?