How long after the armor did you put those things in, though? Perhaps you just didn't notice the armor disappeared until now?
The game is programmed to clear out and refill any chests that are flagged to respawn if you have been away from the area for three game days or more.
If you did leave the armor in the chest past the respawn timeframe, then it has been erased from the game. Only way to get it back is, as stated, reload a previous save.
Next time, just put the armor on the stand. It looks nice, and you can also get the armor re-scaled for your level when you use it.