Multiple warnings after migrating from OJS2 to OJS3.1

Hello,

I have a single journal OJS installation migrated from OJS2 to 3.1.1-4.

Generally speaking - things are working fine (despite plenty of problems with database encoding) but I’m seeing some PHP warnings with debugging switched on and I would like to know if they should be addressed or can be ignored?

Warning:  Declaration of PKPUsageEventPlugin::getEnabled() should be compatible with LazyLoadPlugin::getEnabled($contextId = NULL) in .../www/lib/pkp/plugins/generic/usageEvent/PKPUsageEventPlugin.inc.php on line 0

Warning:  Declaration of DRIVERDAO::setOAI(&$oai) should be compatible with PKPOAIDAO::setOAI($oai) in .../www/plugins/generic/driver/DRIVERDAO.inc.php on line 19

Warning:  Declaration of CustomBlockPlugin::getBlockContext() should be compatible with BlockPlugin::getBlockContext($contextId = NULL) in .../www/plugins/generic/customBlockManager/CustomBlockPlugin.inc.php on line 0

Warning:  Declaration of CustomBlockPlugin::getEnabled() should be compatible with BlockPlugin::getEnabled($contextId = NULL) in .../www/plugins/generic/customBlockManager/CustomBlockPlugin.inc.php on line 0

Warning:  Declaration of SubmissionFileDAO::fromRow($row) should be compatible with PKPSubmissionFileDAO::fromRow($row, $fileImplementation) in .../www/classes/article/SubmissionFileDAO.inc.php on line 23

Warning:  Cannot modify header information - headers already sent by (output started at .../www/lib/pkp/plugins/generic/usageEvent/PKPUsageEventPlugin.inc.php:0) in .../www/lib/pkp/classes/template/PKPTemplateManager.inc.php on line 867

Warning:  Cannot modify header information - headers already sent by (output started at .../www/lib/pkp/plugins/generic/usageEvent/PKPUsageEventPlugin.inc.php:0) in .../www/lib/pkp/classes/template/PKPTemplateManager.inc.php on line 868

I’ve upgraded the system via a command line using fresh OJS files so there shouldn’t be any leftovers from older versions.