Why does the balance of bitcoin drop to 0 after 150 outgoing transactions?

Question

bitcoin

There is a server where bitcoin-cli OS Ubuntu is raised.
The service is a merchant, and so we noticed such a dependence, with large requests, the balance drops to 0 until all transactions go to the network (about 150 transactions), then it gradually levels off, but still then falls .
Moreover, when the command shows a trifle bitcoin-cli getbalance, and if you look at bitcoin-cli listaccounts, it will show true information how much money is in each account.
What to do, the service stops working, because globally the bitcoin client returns an error that there is no money in the account