wifi intermittent, frequent connection drops

[simian]

Hi,

I am a newbie using mint 18.3 mate

My wifi is very unstable, the connection drops frequently while wifi keeps working on my phone and my very old win 7 laptop. There are also no wifi problems when i boot my linux laptop in win 10, so it doesn't seem to be a hardware problem.
The drops can occur after a few seconds or after more than an hour. Sometimes they last a few seconds, sometimes the connection never comes back. Sometimes restarting the network manager allows me to reconnect, sometimes I have to reboot, sometimes I have to reboot several times before I can connect again.

- I bought a TL-Link WN725N hoping that it would improve the reception and hence the connection, but I notice no difference.
- I disabled power management of the network manager in /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf, but that made no difference
- I disabled ipv6 on my connections, that made no difference
- https://itsfoss.com/speed-up-slow-wifi- ... on-ubuntu/ suggested that it might be a bug in the debian avahi daemon, and according to their recommendation in /etc/nsswitch.conf i changed the line
hosts:          files mdns4_minimal [NOTFOUND=return] dns mdns4
to
hosts:          files dns
But that didn't solve the problem either.
- I'm using vpn, but I tested without vpn, that didn't make a difference.

My configuration is summarized here: https://termbin.com/tcv2
The output of cat /var/log/syslog | grep error is attached.

Suggestions?

Thanks!