PCB etching gone bad
I found the answer to the problem. It was not the etching or UV process that was the issue. It turns out that the solution of NaOH was more concentrated than it should have been, so that it took off more photoresist and etching through parts of the copper. This made the copper oxidize so that the board got oxidation marks and the traces was etched away because of the missing photoresist film.

Below is a newly etched board with a lower concentrated NaOH solution. It turned out great!