How is this possible?

is this object visible or not? can I trust Katalon or not?

You can read the source code of both keywords:

If you read the source carefully, both keyword return false when the target element is not found. You should find that verifyElementNotVisible is NOT a simple logical inverse of verifyElementVisible.

Would you argue that the naming is not appropriate? Let me give you +1.

I personally never use those keywords named in a pattern “\w+Not\w+” because they behave differently from what I expect. They confuse me.

naming is defiantly not appropriate.
I’m a simple user. The only code I understand is the code recorded by actions I’ve made or code written directly by me. I saw the code of both keywords and did not understand them at all. if verifyElementNotVisible is not a simple logical inverse of verifyElementVisible then who ever created these keywords should have given them a different name and not expect the common user to dive into the source code.
Thanks a lot for your answer. from now on I will stop using the “NOT” keywords.

Perhaps add your voice to this thread…