The GBL algorithm. I think it hates me. I recently changed my team from Electabuzz, Pidgeot, and Golbat to Electabuzz, Magmar, and Alolan Sandslash. The new team was perfect. It was effective against almost all of the people I fought. Then, after around 10 battles, it changed. Suddenly, I was lucky to win 1 battle out of the sets of 5. It seems like as soon as the algorithm learned what I could fight effectively, it changed my opponents to those I can not beat with the new team.