Clarification: puj is still a valid noun. puj being a noun was not an error.

Someone noticed the fact that the original verse in the 1st edition of paq'batlh was our only source of the noun puj "weakness". The lines were revised because Dr. Okrand was dissatisfied with the interpretation the Klingon translation imposed on the English, which could be interpreted in other ways. A discussion with the editors clarified that the intended meaning of "battling against fear and weakness" is "battling to demonstrate that they're not fearful and weak", and the Klingon version was revised accordingly. The removal of the only example of puj as a noun was incidental.

[...] Some of these lines may have been our only examples of certain constructions or word usages, but I think it should be clear whether the lines were revised because they broke grammatical rules or contained errors, or whether (as in the case of puj) the edit was incidental to the noun/verb in consideration. — (Message to the mailing list of June 23,2022, by David Yonge-Mallo)