Bad business requirements. Same way business partners can introduce bugs with not the greatest business requirements, it can also cause automation to fail.
Hear me out. My test didn’t fail an assertion, and it didn’t throw an exception or crash, however, it didn’t test the correct things, it didn’t check the correct workflows. So, by all accounts it failed because it didn’t provide value or cover any actual business need.
If a work request says to validate ‘X’ but the end user or stakeholder wanted ‘Y’ covered. I’d consider it a failure. At best it brought nothing of value, at worst, it brought a false sense of confidence/security around a project.