network manager does not connect to AP anymore

[Olli Ries]

network manager does not connect to my AP anymore, tries to authenticate and then asks for a password (of a previously connected wifi network). Upon entering the right password manually and/or verifying the stored password is correct the connection still fails.

I have not been able to get a concise list of actions that get me connected, but a wild mix of:
rmmod iwlmvm iwlwifi
modprobe iwlmvm iwlwifi
killall wpa_supplicant
iwlist scanning
(dis-/enabling networking in NWmgr)
(dis-/enabling wifi in NWmgr)

gets me back online

[Olli Ries (ories)]

uname -a:
Linux minimie 4.2.0-16-generic #19-Ubuntu SMP Thu Oct 8 15:35:06 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

lsb-release:
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=15.10
DISTRIB_CODENAME=wily
DISTRIB_DESCRIPTION="Ubuntu 15.10"

[Olli Ries (ories)]

data from a series of failed attempts, unloading & loading the drivers

[Olli Ries (ories)]

HW is a Dell XPS 12 -9Q33

[Olli Ries (ories)]

downgrading the respective firmware to an older release helped.

the system was loading iwlwifi-7260-15.ucode which seemed to be the source of trouble. Removing any firmware but iwlwifi-7260-10.ucode allows me to reliably connect to my network again.