INA828: INA828 output offset, strange behaviour

Tool/software:

Hello !

Here I have very simple gain 10 inst amp. Input is from piezo sensor (about 4nf). But with UNCONNECTED input I get about 15mV AC hum to output AND about 8mV DC offset.

PCB layout is "by the book", power supply +-12V.  There is a slight difference at power voltages, something like +12.1 and -11.9

Probably Im totally missing something here. Have changed all the components twice and check PCB million times over. Any suggestions ?