[Evolution] Address Book errors

[Douglas Summers <ajgringo619 cox net>]

(Evolution 3.28.5, Mint 19, using hotmail.com account)

This just started to pop up in the last couple of weeks. My logs get
flooded with this message, until I kill all Evolution processes:

Dec 19 16:54:34 evolution-calen[1812]: /build/evolution-ews-
Db3ojN/evolution-ews-3.28.1/src/server/e-ews-notification.c:581: Unable
to retrieve events for this subscription.  The subscription must be
recreated., The events couldn't be read.

After I kill Evolution, I then delete all address books in
~/.cache/evolution/addressbook. When I restart Evolution, the address
books are reloaded with no problems.

Any ideas what could be wrong? I haven't added any new contacts in a
while.