Recently when playing I've noticed, that both Wither Skeletons, and Blazes completely stopped spawning (except when spawned by spawner). I used to play this save on 1.12.2, and everything was fine. Now I've changed version of  the game to 1.14.3, and I'm not sure when exactly this happened, but I don't think it's because of changing the version, since mobs like dolphins, pillagers,  villagers, and foxes appear normally. I've noticed, that some people already had problems like this, but none of the solutions I've found worked for me. I also tried recreating the situation on another save, but everything there worked normally. I don't know what to do anymore, but I hope that someone will help me with this.