EOleException - A connection with the server could not be established

Tracking down another problem we discovered regular error messages in the Windows application event log:

#1: EOleException - A connection with the server could not be established @ cs:0000000000B7D84A
Stack trace:
[...]

The exceptions are thrown every hour. There are no scheduled tasks defined.

Version 2017 Update 4. 

What could be the reason? Which server? Which connection?