"A post type mismatch has been detected" Error when updating custom post

I have started getting this error when updating a custom post type on a clients site. I've never seen this error before and can't find any reference to it in Google search. Can anyone point me in the right direction?

Topic errors custom-post-types Wordpress

Category Web

1
answered at

I think that there is a problem with the theme. Updating it to the latest version will solve the issue. A number of users have also faced the same problem with a theme on Theme Forest. The developer has fixed it by releasing a new update. enter image description here

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