not able to control volume via iphone locked screen/nor in spotify application

[MyskoSanka]

Plan

Premium

Country

Slovakia

Device

iPhone 6

Operating System

iOS 12.4 (even previous it did not work)

My Question or Issue

I have connected spotify via AVR Denon x2500h and using iphone ( just updated iOS 12.4), Spotify app ver. 8.5.18.851 (just updated). It worked well to remotely control volume approx. 2 weeks ago. nothing has been changed, just stopped working. I have "Devices Lock Screen function" ON. Any Ideas I could try to get this fixed? 

Thanks a lot, it's getting annoying to control volume and songs by 2 applications (spotify for song + denon app for volume)