Having started this thread and seen all kinds of issues with WiFI on 8.0 and the 8.1 Dev Preview, I will now say that after having flashed my phone back to 8.0 and going through all the pain of getting Sprint's official 8.1 (and firmware) I have not seen this happen for over 2 weeks!
Now, of course, that process also deleted all apps/settings/etc. so it might not have been that but I have to believe getting to the latest sprint/Samsung firmware is key.
**edit**1/27/15 It just f'n happened again. I guess I spoke too soon! LOL
Is this a "known" issue yet with Sprint? Awful lot of people experiencing it! Including me -- have had the phone for over three months, and it just started happening last week with a known Wifi network I've been for the life of the phone.