I recently started having this problem with my MacBook Air 2013 (i7/8GB) running the latest High Sierra:
Sleep itself works perfectly fine. If I wake up the device within the standbydelay of 3 hours, there is no issue. As soon as the device goes into deep sleep (also called standby/hibernation?), for example if it was sleeping overnight, I get the following issue:
I see the Apple logo appearing shortly with a chime, then I get a line across the screen and the screen goes dark as if I forced the device to turn off. After that, the device chimes again and it boots normally but it doesn't go back to where I started. It seems to perform a full reboot.
I already tried disabling some sleep related features like Power Nap. I cleared my NVRAM and SMC. Apple Hardware Test completes successfully.
Anything else I could try here? Oh, and I use APFS Encrypted with File Vault 2. Could this be the culprit?