Duplicate errors

In my Google webmaster tools we are suddenly getting duplicates any ideas what is causing it please?

HTML Improvements

Last updated 7 Oct 2018

Addressing the following may help the user experience and performance of your site.

Meta description Pages

Duplicate meta descriptions 57

Long meta descriptions 0

Short meta descriptions 18

Title tag Pages

Missing title tags 0

Duplicate title tags 78

Long title tags 0

Short title tags 0

Non-informative title tags 0

Non-indexable content Pages

We didn't detect any issues with non-indexable content on your site.