I do. New S5 - about 3 weeks old. SM-G900I (Australian)
Wifi is off and just clicking it goes to that half greyed out state. If I exit and come back to settings it's back to off.
Haven't installed heaps of apps:
1) No adblockers
2) Not rooted
3) No Xposed framework
4) 3G/4G network still appears to be working ok once Wifi goes off
5) *Seems* to happening in the evening (not 100% sure on this)
6) Airplane mode on/off fixes it (as does reboot)
7) There is no connection optimiser that I can find.
8) Don't think it was happening until recently (i.e. when new was OK).
9) I do use MultiWindow occasionally (usually web links in Gmail opening Chrome)
Can't really afford to factory reset at this point.
I know it's a pain to factory reset because you lose everything and have to start again, but it is a last resort and may solve the problem for you.
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