Sent from my Nexus 7 2013
I think I may have found something. In /system/etc/wifi/wpa_supplicant_overlay.conf
Theres a line:
disable_scan_offload=1 (has to do with allowing scanning to be offloaded to the driver)
This line didn't exist in 4.2.2. Change it to 0 and reboot and see if your wifi scanning doesn't stop working after a while.
I just ran an errand and it connected perfect when I got home which is usually when it stops working.