These are defects or bugs, found while doing regression testing. Automation does great help for regression testing, find regression defects and even help to verify them.
I will explain in brief about regression testing first and how it's done.
So what is regression- Here I am taking UI regression as an example and same goes for REST APIs or data layer (ETL) side regression testing.
Lets assume, first screens is totally developed and testing team prepared all test cases as per feature and UI. You found defects, you raised it and move on to next screen. When developer find time and pick up that defect and fixed it. You get that fixed, you try to reproduce that defect. Voilà, its working as per requirements, you verified that defect and close it. In this case you just test the that particular defect, not the entire feature. Now that fix code may hamper the existing functionality which were working fine earlier.
So for ensuring that fix doesn't affect existing code, you need to test entire functionality or screen. During this testing you found few other defects these are called regression defects and this testing acitivity called regression testing.
How regression testing done- Here automation come handy. When you test any functionality whether it's on UI/Rest Apis/data side, you automate the test cases and run them regularly. When new fixes come, all those automated test cases run daily and check if everything working fine. If does not, you found regression defects. You also find out earlier failed test cases are working fine with fixes.
Hope this help.