Hi @Tadej_Lukovnjak welcome to Zwift forums
Have you read through the latest Android FAQ? In particular you may have to install the ANT system drivers.
The other thing to know is that support for controllable trainers using the ANT protocol is still new. It’s possible that your brand / model of tablet hasn’t been tested for compatibility yet.
What happens if you pair over Bluetooth LE instead? Does that give better results?