Those that are still having drain issues even after the update, can you please go to About Phone -> Software Information, what does it read under Baseband Version? I'm running Oreo with the baseband version ending in ERG2 and no battery drain issues at all.
And now I just learned that a new bootloader (ERGE) and modem (ERGC) have been released. Downloading them and will flash soon.
Mine ends ERE8 on S7 Edge UK and have the problem. This is Oreo first OTA update in April.
Well, that's the problem. That's the old modem. You need ERG2 at least and which is a zip file you flash using TWRP. If your phone is pure stock, there's no way to do that. That's what's bothering everyone. The modding/xda community is able to update to the latest files which Samsung is not pushing to all its customers.
If you want to solve the battery drain problem, you'll need to install custom recovery TWRP (lots of guides and youtube videos online) then flashing the latest bootloader and modem zip file. I can help those interested.