network trouble after upgrading from Debian Jessie to Stretch

Question

I use a Lenovo U31-70 with a Qualcomm Atheros QCA6164 Wireless Network Adapter using the ath10k_pci driver module.

I recently tried to upgrade my Jessie installation to Stretch by altering my /etc/apt/sources.list to point to the stretch repositories, and then running apt-get update and apt-get upgrade. This ran for quite a while and got into a loop where the restart of network-manager timed out, and finally hanged my system hard enough to make it non-responsive.

After hard reboot, the system booted up and connected fine to my wifi, but running any apt-get operation finally ended up in the same state.

I decided to take drastic action; backed up my /home and installed Debian Stretch with non-free additions from scratch.

Now apt-get works fine, but the system won't shut down cleanly. Sometimes I will get a black screen with network operations trying to finish but never succeeding.

[*   ] (1 of 2) A stop job is running for Network Manager (4min 49s / 5min)
[*   ] (2 of 2) A stop job is running for WPA supplicant (5 min 2s / 6 min) 

If I loose a network connection, I'm not able to re-establish it or switch to another network.

# service wpa_supplicant stop

takes about two minutes to return and so does

# service network_manager stop

Has anyone else experienced trouble with network managing in Stretch? Is there anything I can do about this?

The output of ip a is

...
3: wlp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
  link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff
  inet 192.168.0.17/24 brd 192.168.0.255 scope global dynamic wlp320
    valid_lft 3450sec preferred_left 3450sec
  inet6 xxxx::xxxx:xxxx:xxxx:xxxx/64 scope link
    valid_lft forever preferred_left forever

/etc/network/interfaces is very short

source /etc/network/interfaces.d/*
auto lo
iface lo inet loopback

and /etc/network/interfaces.d is an empty directory.