There is a lot more discussion on the seaweed (sargassum) issue at www.playa.info
and on Trip Advisor Playa del Carmen forum or Cozumel forum.
In general, the sargassum is floating along in various sized mats, pushed by current and wind. East facing beaches are generally hit the hardest. West facing beaches usually less, but storms can disrupt that pattern.
Some days it is not present, some days it is. Accumulations on the beaches can also depend on how much work is being put in to either remove or bury the stuff.