With the release of the Sultans ascend and season six, the quality of the game experience has reduced significantly. Some of the problems/bugs I experienced include the game working a lot slower than after the season four changes, explosive ships not targeting properly and exploding on contact with enemy ships and cavalry units, mainly scouts (khan, scout and warrior scout) having their animations frozen for short periods of time when descending large terrain.
With the Ottomans, I found a glitch that happened in the later game where some or even all the military schools would glitch and not finish producing a unit, displaying that it is almost done but never finished.
With the Japanese, there is a problem with the ########### gunsmith landmark, where it does not display the amount of stockpile points you have.