We’ve all been in the situation where resources seem scarcer than they ought to be, but please keep in mind that resources never disappear by themselves, and the game never makes purchases on the player’s behalf. 

Resources are always used to perform an action in the game like upgrading and creating buildings or units, so that’s the first and best place to look for an explanation. Is something cooking in your Barracks, or perhaps a building is being upgraded? Or has any defense building recently been repaired? 

Another place to look at is whether you recently instant-completed an operation (for example, building upgrade, troop summoning). When you do an Instant Complete, we first try to use all the resources you have in your City, and if they are not enough, we will calculate the Gem cost for buying the missing resources and well as the time required, then propose a total Gem cost for you to decide. That's why it's common to find out that you have 0 resource left after an Instant Complete operation, but we believe this design is at a player's best interest to use what they already have first to minimize their gem cost. 

If you can’t find any clues in your account, check your Battle Report t o see if some resources have recently been stolen from you.