Posts republishing every day.. plugin??

Hi, I operate a blog using wordpress and it’s been running for a few years now. However just recently it started republishing posts daily. It is INCREDIBLY annoying for users. I think it’s a plugin issue. I haven’t installed any new plugins recently, and it takes place over several hours so it’s hard to pinpoint. However I just switched themes so it’s possible the last theme was muting the issue even tho it has been there the whole time with a past plugin.

Has anyone experienced or heard of this issue before?

Cheers and thanks for your help!!