WiFi issues since version 5.0

[Avishay28]

Hello,
Two months ago I upgraded my android version to 5.0.1, since then wifi problems start to appear.
There are two problems:
1) When the phone is sleeping, the wifi disconnect. once I wake the phone, even if it still locked, the wifi turns on again after 1 second. (I checked the advanced settings and "keep wifi on during sleep" is on "always").
2) Once I go from the wifi zone and come back after a while, I can't connect to the wifi. it just keep scanning, and when I tap on it to see available networks it just shows white page (switching wifi on and off doing nothing).
This problem can be solve by turning airplane mode on and off, but it only helps for one time - once I go away and come back to the same wifi zone I need to do it again.

*I tried factory reset, doesn't help.
*I flashed another rom, from HD revolution to ViperOne, and now my android version is 5.0.2, doesn't help.
*This problem happens in every router, not only in a specific one.
Maybe going back to the stock recovery will solve the problem, but I don't think so.

Thanks in advance