Sometime between Aug 23. and Sept 11. the following issue started: Selecting any menu item to J!mailAlerts (JmailAlerts, Frequencies, Sync,...) leads to a
An error has occurred.
0  operator not supported for strings
page, screenshot here:
JMA has been installed new (over the existing installation), but that did not help. Any thoughts, please, what should I check?
Joomla 3.8.12, JMailAlerts 2.5.4