I got severall probs with Wlan and Volumio 2 decribed in an other topic.
I also noticed, that WLAN connections from PC to Volumio are more stable then
from an Android device to Volumio.
Now I found in an other forum the following information:
»Android and Chrome forces the use of googles DNS servers at 22.214.171.124 and 126.96.36.199
Go to your wifi settings and long-press and add your local router (or the Pi acting as a local router) address in place of the google ones and use a browser other than android default or chrome.«
I tried it and gave Android devices in Prefered (First) DNS the same IP then the rooters IP as usually done on the PC.
The Wlan connection now is more stable and faster and disconnections seldom.