Losing control of android device over Spotify Connect

[monoaudiostereo]

Hi. I have an issue with Spotify Connect. I wanted to do a "Ghetto Chromecast audio" so I took my old Galaxy Ace 2 and connected it to the speaker and power source. I wanted it to be hooked there 24/7 so I can use Spotify Connect anytime to play/stop/change music anytime I want. The problem is that when my android device screen goes off, Im losing control of it on my PC. I can see on my PC that the music is playing on that android device, but when I fast forward the song, change it or whatever, it suddenly stops playing on android device and continues to play on PC. After that my PC still shows that there are available devices for Spotify connect but when I click it it can see my Ace 2 but it says "cannot connect to the device". It becomes available again when I unlock my phone.

My Ace 2 is clean, any bloatware is removed, spotify is the only thing installed there. Any power saving modes are disabled. I checked Spotify Connect on my second android phone - Motorola Moto E 2 and Im having the same issue. How do I fix this?

Ace 2 is running 4.1.2. Moto E 2 is running 6.0

[Joe]

I know you said power saving modes are disabled but it's worth checking just in case - 

• Wifi/More/keep wifi on during sleep - set to always
  Battery - Power saving modes off
  Battery/App power saving/details - make sure Spotify is not listed. If it is, select and disable

[monoaudiostereo]

Double checked. No issue there.