It is lilely that upon waking up your PC from sleep mode that the BIOS kind off 'auto resets' the fan settings which is why the fan speeds drop to (most likely) match the current temperatures in the PC.
How to stop it, well I don't really know how...
It may be an actual issue with the board or that the board just doesn't support the option, I'll see if I can find some resolutions however but I have explained to you what it might be.
Thanks, I appreciate the advice. I'll keep trying settings or maybe get a fan speed program if I can't figure it out.