Okay so, I bought the classic fishing skill in Silvermoon on my lvl 8 BE paladin (realm Suramar if that’s important). I went to fish in Eversong Woods and I’m only catching Raw Slitherskin Mackerels, and getting no skill increase. My cooking, blacksmithing, and mining are also classic and they all increase fine. I tried several pools/rivers in the area and the same issue presents. I submitted a ticket but was told it’s definitely a bug and to submit it here.
Edit to add: This also occurs in/around Silvermoon, but I get raw brilliant smallfish and long jaw mudsnappers