Network Error on Contact Search Results page change
[SOLVED] Yes found an answer with the help of the CiviCRM team - see https://lab.civicrm.org/dev/core/issues/963

The issue is MySQL configuration after upgrading, which adds ONLY_FULL_GROUP_BY to variable sql-mode.  There is a link to a patch but I found it straghtforward to remove this by adding the following line to my.cnf

sql-mode="STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"

Hope that helps.