Did you check the daydream setting? If it's turned on, try turning it off.
Also, do you have an app that may be waking the screen? For example, I know that the text messaging app textra has a default setting to wake the screen when you receive a message. Maybe you have another app that is doing this? Or are you sure that it coincides with full charge?
And, of course, the other option, if you don't figure it out, is to plug in to charge and just use the wireless charger for short charges. Wired charging *is* better for long term battery life anyway, as wireless charging raises the temperature of the battery pack higher while charging due to inefficiency that normal charging doesn't share.