Help error when rebuilding search index and searching


I am getting the following error incessantly when I try to rebuild my search index:

PHP Warning: Illegal offset type in …/web/ojs-3.1.2/lib/pkp/classes/search/ on line 48

I’m not sure if it is related, but the following error also appears repeatedly in my php error logs:

[Sun Apr 21 01:32:52.568844 2019] [proxy_fcgi:error] [pid 3703:tid 139643852150528] [client] AH01071: Got error ‘PHP message: PHP Warning: Declaration of DRIVERDAO::setOAI(&$oai) should be compatible with PKPOAIDAO::setOAI($oai) in …/web/ojs-3.1.2/plugins/generic/driver/ on line 19\n’, referer: Search | Monthly Review

This appears to trigger whenever a search is initiated.

I should also mention that I have just moved my installation to a new server but I was getting a significant number of errors in my old installation as well.

Many thanks for any help you can offer.