Network connections have gone erratic

[Bret Busby]

Hello.

On one of my computers running Linux Mint Mate 21.2, I, yesterday or the 
day before, did a system update that included an update of avahi, which 
is apparently, a networking utility.

Afterward, the computer, which I have had connected by wifi to a wifi 
modem, and, by USB tethering, to my cellphone for Internet access, both 
devices using 4G cellphone networks with different carriers, to access 
the Internet, with the USB tethering involving "hot plugging" (?), can 
no longer use the USB tethering, which, whilst I set the USB tethering 
to "On", on the cellphone, is automatically severed, with no data shown 
as being transferred, and, the NetworkManager Applet shows the wifi 
connection to the wifi modem, to be in an endless loop of dropping out 
and reconnecting.

I can send and receive data, but, it is erratic.

I do not know whether the networking connections failing, is due to the 
avahi upgrade, or just coincides with the timing, but, it is worrying.

Prior to the avahi update, I had not encountered this problem, and, the 
networking connections had been stable.

I had performed an orderly shutdown and reboot, to find whether that 
might fix this, but, it did not fix the problem.

How do I find what is causing this, and, how do I fix it?

Thank you in anticipation.

....
Bret Busby
Armadale
Western Australia
(UTC+0800)
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