This article explains why a player who was added and dropped on the same day does not go to waivers but instead remain free agents.
If your league features a waiver period of one or more days and you see players signed as free agents on the same day they were dropped, it is likely because their previous owner added and dropped them on the same day.
When players are added and dropped on the same day, they will be returned to the player pool as free agents rather than being placed on waivers. Previously, it was possible for a Fantasy owner to "tie up" players other teams may be interested in by adding and dropping them on the same day. This is now prevented by allowing these players to remain free agents.
If an owner adds players and then drops them the following day, the player will be subject to your league's waiver rules.
Note: A manager may add a player twice in the same day. If that manager drops the player a second time, they will be locked from adding that player again until the following day. The player will return to the player pool as a free agent.