Error: USB setup failed

[vicdavery]

Hi,
Been enjoying the player for some time. I have a Nokia 8 and Dragonfly Red DAC.
My Nokia has recently upgraded to Android Pie. Since then I have been experiencing an annoying issue. If I pause playing and leave it for a couple of minutes, when I attempt to resume playing I get a "Error: USB Setup failed". 
The only way to clear it seems to be to detach the DAC and reattach. 

Can you help, please?
Thanks.
Vic.

[MuseFred]

You should disable the powermanagement für the USB Audio Player app in the system settings. By default, Android tries to minimize energy consumption in idle mode for all apps. Therefore you have to turn off the automatic for some apps.

[vicdavery]

You should disable the powermanagement für the USB Audio Player app in the system settings. By default, Android tries to minimize energy consumption in idle mode for all apps. Therefore you have to turn off the automatic for some apps.

Thanks for your input. Sadly it has made no difference. 
I've turned off Battery Optimisation for USB Audio Player and removed it from the Restricted Apps.
Unless there's somewhere else.......