@Salam_Al-Khammasi I saw you got help with your issue. The same did not work for us.So the two errors are probably not related. For us it is only back issues past a certain dat/year, for you, as I understood your post, it was all issues/articles.
@asmecher Turned on display errors and got this:
Fatal error: Uncaught Error: Call to a member function getDisplayName() on null in /lib/pkp/classes/galley/Galley.php:160
Followed by a 28 step stack trace that is mostly the same with or without the modifications to RecommendBySimilarityPlugin that you suggested to Salam above (which resultet in 29 steps). I included the trace with the original unmodified plugin below:
#0 /cache/t_compile/62db40a58450975d215414057ce5369d0501eb8b^9190456890661656c2db668fc3c363ee4354c517_0.app.frontendobjectsgalley_link.tpl.php(71): PKP\galley\Galley->getGalleyLabel()
#1 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_template_resource_base.php(123): content_6530dc5b01f504_33444509(Object(Smarty_Internal_Template))
#2 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_template_compiled.php(114): Smarty_Template_Resource_Base->getRenderedTemplateCode(Object(Smarty_Internal_Template))
#3 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_internal_template.php(384): Smarty_Template_Compiled->render(Object(Smarty_Internal_Template))
#4 /cache/t_compile/62db40a58450975d215414057ce5369d0501eb8b^7cf1cd52b8ba8108de77f197078de34b733dd394_0.app.frontendobjectsarticle_summary.tpl.php(128): Smarty_Internal_Template->_subTemplateRender(‘app:frontend/ob…’, NULL, ‘62db40a58450975…’, 0, 3600, Array, 0, true)
#5 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_template_resource_base.php(123): content_6530dc5b06a767_04114008(Object(Smarty_Internal_Template))
#6 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_template_compiled.php(114): Smarty_Template_Resource_Base->getRenderedTemplateCode(Object(Smarty_Internal_Template))
#7 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_internal_template.php(217): Smarty_Template_Compiled->render(Object(Smarty_Internal_Template))
#8 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_internal_template.php(386): Smarty_Internal_Template->render()
#9 /cache/t_compile/62db40a58450975d215414057ce5369d0501eb8b^26de9c47ced54328a8eb56e39bb4d4079aa049c6_0.app.frontendobjectsissue_toc.tpl.php(48): Smarty_Internal_Template->_subTemplateRender(‘app:frontend/ob…’, NULL, ‘62db40a58450975…’, 0, 3600, Array, 0, true)
#10 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_template_resource_base.php(123): content_6530dc5b0334c9_48846696(Object(Smarty_Internal_Template))
#11 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_template_compiled.php(114): Smarty_Template_Resource_Base->getRenderedTemplateCode(Object(Smarty_Internal_Template))
#12 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_internal_template.php(217): Smarty_Template_Compiled->render(Object(Smarty_Internal_Template))
#13 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_internal_template.php(386): Smarty_Internal_Template->render()
#14 /cache/t_compile/62db40a58450975d215414057ce5369d0501eb8b^fcbc2cabc0d4dff6219d7e4b5d36c1363533cfd8_0.app.frontendpagesissue.tpl.php(144): Smarty_Internal_Template->_subTemplateRender(‘app:frontend/ob…’, NULL, ‘62db40a58450975…’, 0, 3600, Array, 0, false)
#15 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_template_resource_base.php(123): content_6530dc5aea7183_31223773(Object(Smarty_Internal_Template))
#16 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_template_compiled.php(114): Smarty_Template_Resource_Base->getRenderedTemplateCode(Object(Smarty_Internal_Template))
#17 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_internal_template.php(217): Smarty_Template_Compiled->render(Object(Smarty_Internal_Template))
#18 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_internal_templatebase.php(238): Smarty_Internal_Template->render(false, 1)
#19 /lib/pkp/lib/vendor/smarty/smarty/libs/sysplugins/smarty_internal_templatebase.php(134): Smarty_Internal_TemplateBase->_execute(Object(Smarty_Internal_Template), NULL, ‘62db40a58450975…’, NULL, 1)
#20 /lib/pkp/classes/template/PKPTemplateManager.php(1325): Smarty_Internal_TemplateBase->display(‘frontend/pages/…’, NULL, ‘62db40a58450975…’, NULL)
#21 /pages/issue/IssueHandler.php(138): PKP\template\PKPTemplateManager->display(‘frontend/pages/…’)
#22 [internal function]: APP\pages\issue\IssueHandler->view(Array, Object(APP\core\Request))
#23 /lib/pkp/classes/core/PKPRouter.php(334): call_user_func(Array, Array, Object(APP\core\Request))
#24 /lib/pkp/classes/core/PKPPageRouter.php(277): PKP\core\PKPRouter->_authorizeInitializeAndCallRequest(Array, Object(APP\core\Request), Array, false)
#25 /lib/pkp/classes/core/Dispatcher.php(165): PKP\core\PKPPageRouter->route(Object(APP\core\Request))
#26 /lib/pkp/classes/core/PKPApplication.php(387): PKP\core\Dispatcher->dispatch(Object(APP\core\Request))
#27 /index.php(21): PKP\core\PKPApplication->execute()
#28 {main} thrown in /lib/pkp/classes/galley/Galley.php on line 160