First you restart and check again.
Then you contact pixel support.
To my knowledge, there has not been a single incident where coins where somehow missing without a reason, so if your case is the first, please give feedback here, what pixel support told you.
It is important to know that to help other players.
So far, nobody ever posted a response by pixel here that stated that the game had eliminated coins or gems. That’s where my knowledge so far comes from. 😉
That is why I would really like you to share whatever reaction you get from pixel support with us.
In most cases players spend the coins by mistake or the amount was not correctly shown but corrected with a restart.