Hello guys! my cardian deck is pretty good but he would be a lot better without this big bug!! when i summon one of my synchro cardian monster and when i activate de-synchro half of the time dont know why de-synchro send the synchro to the extra deck BUT DONT SUMMON MY CARDIAN THAT WAS MATERIAL SYNCHRO AND THEN I LOSE THE MATCH...thats very unnerving!! so please can you correct this bug with all cardian synchro monsters? Thanks in advance~~
You have to make sure the cardians used for the synchro summon were summoned properly prior. If they were not then cards like de-synchro cannot summon them.

When you summon a Cardian with Moonflower or the like that ignore summoning conditions, you cannot special summon them back. And De-Synchro is an "Summon all or nothing" card, so if you cannot summon one of the materials, you cannot summon any. Same if one material is no longer in the graveyard, maybe that was your problem as well.