ath9k driver not working after kernel update

Question

I'm on Ubuntu-Gnome 16.04, I have two kernel version installed, that are 4.15 (4.15.0-24-generic) and 4.13 (4.15.0-24-generic). When I boot into the older one (4.13) everything works fine. But after the kernel update (booting into 4.15) the WiFi adapter is not claimed by the driver, the driver is not loaded. Trying to load the driver manually via modprobe ath9k fails, hinting that the driver is not found. Here is the output of dkms status:

bbswitch, 0.8, 4.13.0-43-generic, x86_64: installed
bbswitch, 0.8, 4.13.0-45-generic, x86_64: installed
bbswitch, 0.8, 4.15.0-24-generic, x86_64: installed

I think it is strange that the ath9k driver does not appear in this list. This list was obtained while booted into the working 4.13 kernel. Questions:

1. Why is that?
2. How do I get the driver loaded when booted into the newer 4.15 kernel?

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lspci -knn | grep Net -A3; rfkill list

03:00.0 Network controller [0280]: Qualcomm Atheros AR9285 Wireless Network Adapter (PCI-Express) [168c:002b] (rev 01)
    Subsystem: AzureWave AW-NB037H 802.11bgn Wireless Half-size Mini PCIe Card [AR9002WB-1NGCD] [1a3b:2c37]
    Kernel driver in use: ath9k
    Kernel modules: ath9k
0: asus-wlan: Wireless LAN
    Soft blocked: no
    Hard blocked: no
1: asus-bluetooth: Bluetooth
    Soft blocked: no
    Hard blocked: no
2: phy0: Wireless LAN
    Soft blocked: no
    Hard blocked: no
4: hci0: Bluetooth
Soft blocked: no
Hard blocked: no