It seems my BTC2 balance are decreasing. I have 15.1 but now only 14.71
The problem is that a zBTC2 mint is missing/not being displayed in the balance.
You mentioned in a PM that you tried to mint in order to stake. Using the zBTC2 minting is not staking, as a matter of fact it reduces the balance that you have available for staking and just prepares the amount that you mint to be sent to someone anonymously.
Everyone: For the time being don't mess with the Privacy tab's
zBTC2 minting in the v.2.0.0 "preview" version unless you know what you're doing.
Recovery:This has happened to you and one other person so far. There's a way to recover the missing zBTC2 mint but right now it's a bit more technical than it could be. A future version will make it easier.
The first thing to try is to go to the Privacy Tab and then click Reset and Rescan, in that order, a couple of times. This might already fix the problem and the zBTC2 could appear within a few minutes after you've done that.
If not, you can try the following:
Please be aware zBTC2 signatures are stored in the wallet.dat used at the time of minting, so if you have loaded an older/different backup since then, or used this wallet on more than one machine, you will want to check your other wallet.dat backups from around the time of minting. You may need to run the below steps on all relevant wallet.dats.
First, go to tools -> debug console and enter the following commands in this order:
getarchivedzerocoin
reconsiderzerocoins
resetspentzerocoin
resetmintzerocoin true
Then, go to the Privacy tab and use the Reset and then ReScan buttons.