Same issue on stable Oreo! Only reboot helps. I am thinking about returning my phone. :(
So, I changed "Keep Wi-Fi on during sleep" to "Always" in settings and it seemed to work for now. Guys, try this and tell if this solved the problem for you.
Getting the same fault on Oreo. Wifi keeps dropping out
before the 8.1 update wifi was working fine in my room and the wifi router is kept in other room but after update its having issues i have stand very near to wifi router to get connectivity or the phone says wifi has no internet connection