He mentions almost being fired during the third season for not being punctual in this
interview at Startrek.com. Google couldn't find anything more specific, but it lines up with the episodes mentioned.
There were other sources online and off that mentioned that before. Apparently the original idea was to have Kim killed off the show, but last minute, Kes (Jennifer Lien) got the boot. Many believe this had to do with Wang being nominated one of tv's most beautiful people that year and they thought it'd hurt the ratings. I'm not sure how true that is, but I wouldn't be too surprised. I liked Harry, but to me, he really outlived his use and purpose on the show and should have had an exit, whether it be death or something else.