Which phone was it? And have you followed the correct process to get to that “debugging kernel"

It's actually a MSG I get after doing a hard reset on my flip 3. After reset it says "could not debug kernel, if you're seeing this MSG contact the vendor" it says that MSG in the reset log file. 

Was your phone rooted? or was there any firmware changed by the user?

Anyway, If the phone operated as normal without any issue, then I would let it be.