That's usually indicative of either the connection needing to be reset (2A), or the devices needing to be restarted (2B).
You didnt mention your Roku model # and firmware version (Settings/System/About) or your Android device brand/model/software version
1) Verify screen mirroring of Roku is configured/working properly:
A) Settings/System/Screen mirroring/Screen mirroring mode=Prompt
B) Settings/System/Screen mirroring/Screen mirroring devices/Always blocked=none
C) Settings/System/Advanced system settings/Device connect=Enabled
D) Settings/System/Advanced system settings/Control by mobile devices=Default
E) Always select "Always allow" when prompted by the Roku
F) Test with (another) Android/windows Miracast-capable device
2) Workarounds/solutions:
A) Disable/re-enable WiFi connection of phone/tablet/PC - try again
B) Restart Roku/phone/tablet/PC/modem/router/gateway - try again
C) Switch Roku and/or phone/tablet/PC to 2.4Ghz SSID or 5Ghz SSID - try again
D) Delete all devices under Always Allow - try again
