Keep getting "Eject Disk before removing" warnings

[jlc1978]

Periodically, when my MBP goes to sleep after I close the case, my SD card is dismounted and I get a warning to eject the disk before removing.

I ran Apple Diagnostics and the GB ran the full suite and everything checked out Ok.
Anyone with a similar problem they resolved?

 

[maflynn]

Did you try ejecting the SD before putting the computer to sleep?

 

[jlc1978]

Did you try ejecting the SD before putting the computer to sleep?

Thanks, but that defeats the purpose of the NiftyMini Drive. I never ha this issue under Yosemite; it crop dup under El Capitan even with different cards.