Then rebuilding the semantic data on www.mediawikiwidgets.org I get the following stack trace for about 25 of the widgets. This is the one for the Google Presentation widget but this basically happens for all widgets:
Issue
2016-01-05 18:09:17 phalaris 0212020151020-mw_: [e4dc7de4] [no req] ErrorException from line 27 of /.../w/widgets/ba811dbfd89414d874993a209b5e2eb71ad14d2d.wiki.Google Presentation.php: PHP Notice: Trying to get property of non-object
Stacktrace
#0 /.../w/widgets/ba811dbfd89414d874993a209b5e2eb71ad14d2d.wiki.Google Presentation.php(27): MWExceptionHandler::handleError(8, 'Trying to get p...', '/var/www/htdocs...', 27, Array)
#1 /.../w/extensions/Widgets/smarty/libs/sysplugins/smarty_internal_templatebase.php(180): content_562822b9c0c22(Object(Smarty_Internal_Template))
#2 /.../w/extensions/Widgets/WidgetRenderer.php(131): Smarty_Internal_TemplateBase->fetch('wiki:Google Pre...')
#3 [internal function]: WidgetRenderer::renderWidget(Object(Parser), 'Google Presenta...', 'docid=dcn37mcz_...')
#4 /.../w/includes/parser/Parser.php(3771): call_user_func_array('WidgetRenderer:...', Array)
#5 /.../w/includes/parser/Parser.php(3505): Parser->callParserFunction(Object(PPFrame_DOM), '#widget', Array)
#6 /.../w/includes/parser/Preprocessor_DOM.php(1169): Parser->braceSubstitution(Array, Object(PPFrame_DOM))
#7 /.../w/includes/parser/Parser.php(3322): PPFrame_DOM->expand(Object(PPNode_DOM), 0)
#8 /.../w/includes/parser/Parser.php(1231): Parser->replaceVariables('<noinclude>__NO...')
#9 /.../w/includes/parser/Parser.php(434): Parser->internalParse('<noinclude>__NO...')
#10 /.../w/extensions/SemanticMediaWiki/includes/ContentParser.php(202): Parser->parse('<noinclude>__NO...', Object(Title), Object(ParserOptions), true, true, 1734)
#11 /.../w/extensions/SemanticMediaWiki/includes/ContentParser.php(147): SMW\ContentParser->fetchFromParser()
#12 /.../w/extensions/SemanticMediaWiki/src/MediaWiki/Jobs/UpdateJob.php(136): SMW\ContentParser->parse()
#13 /.../w/extensions/SemanticMediaWiki/src/MediaWiki/Jobs/UpdateJob.php(119): SMW\MediaWiki\Jobs\UpdateJob->needToParsePageContentBeforeUpdate()
#14 /.../w/extensions/SemanticMediaWiki/src/MediaWiki/Jobs/UpdateJob.php(88): SMW\MediaWiki\Jobs\UpdateJob->doPrepareForUpdate()
#15 /.../w/extensions/SemanticMediaWiki/src/MediaWiki/Jobs/UpdateJob.php(57): SMW\MediaWiki\Jobs\UpdateJob->doUpdate()
#16 /.../w/extensions/SemanticMediaWiki/src/SQLStore/ByIdDataRebuildDispatcher.php(171): SMW\MediaWiki\Jobs\UpdateJob->run()
#17 /.../w/extensions/SemanticMediaWiki/src/Maintenance/DataRebuilder.php(247): SMW\SQLStore\ByIdDataRebuildDispatcher->dispatchRebuildFor(56)
#18 /.../w/extensions/SemanticMediaWiki/src/Maintenance/DataRebuilder.php(147): SMW\Maintenance\DataRebuilder->doRebuildAll()
#19 /.../w/extensions/SemanticMediaWiki/maintenance/rebuildData.php(141): SMW\Maintenance\DataRebuilder->rebuild()
#20 /.../w/maintenance/doMaintenance.php(103): SMW\Maintenance\RebuildData->execute()
#21 /.../w/extensions/SemanticMediaWiki/maintenance/rebuildData.php(174): require_once('/var/www/htdocs...')
#22 {main}Issue
2016-01-05 18:09:17 phalaris 0212020151020-mw_: [6dd14303] [no req] ErrorException from line 28 of /.../w/widgets/ba811dbfd89414d874993a209b5e2eb71ad14d2d.wiki.Google Presentation.php: PHP Notice: Undefined index: size
Stacktrace
#0 /.../w/widgets/ba811dbfd89414d874993a209b5e2eb71ad14d2d.wiki.Google Presentation.php(28): MWExceptionHandler::handleError(8, 'Undefined index...', '/var/www/htdocs...', 28, Array)
#1 /.../w/extensions/Widgets/smarty/libs/sysplugins/smarty_internal_templatebase.php(180): content_562822b9c0c22(Object(Smarty_Internal_Template))
#2 /.../w/extensions/Widgets/WidgetRenderer.php(131): Smarty_Internal_TemplateBase->fetch('wiki:Google Pre...')
#3 [internal function]: WidgetRenderer::renderWidget(Object(Parser), 'Google Presenta...', 'docid=dcn37mcz_...')
#4 /.../w/includes/parser/Parser.php(3771): call_user_func_array('WidgetRenderer:...', Array)
#5 /.../w/includes/parser/Parser.php(3505): Parser->callParserFunction(Object(PPFrame_DOM), '#widget', Array)
#6 /.../w/includes/parser/Preprocessor_DOM.php(1169): Parser->braceSubstitution(Array, Object(PPFrame_DOM))
#7 /.../w/includes/parser/Parser.php(3322): PPFrame_DOM->expand(Object(PPNode_DOM), 0)
#8 /.../w/includes/parser/Parser.php(1231): Parser->replaceVariables('<noinclude>__NO...')
#9 /.../w/includes/parser/Parser.php(434): Parser->internalParse('<noinclude>__NO...')
#10 /.../w/extensions/SemanticMediaWiki/includes/ContentParser.php(202): Parser->parse('<noinclude>__NO...', Object(Title), Object(ParserOptions), true, true, 1734)
#11 /.../w/extensions/SemanticMediaWiki/includes/ContentParser.php(147): SMW\ContentParser->fetchFromParser()
#12 /.../w/extensions/SemanticMediaWiki/src/MediaWiki/Jobs/UpdateJob.php(136): SMW\ContentParser->parse()
#13 /.../w/extensions/SemanticMediaWiki/src/MediaWiki/Jobs/UpdateJob.php(119): SMW\MediaWiki\Jobs\UpdateJob->needToParsePageContentBeforeUpdate()
#14 /.../w/extensions/SemanticMediaWiki/src/MediaWiki/Jobs/UpdateJob.php(88): SMW\MediaWiki\Jobs\UpdateJob->doPrepareForUpdate()
#15 /.../w/extensions/SemanticMediaWiki/src/MediaWiki/Jobs/UpdateJob.php(57): SMW\MediaWiki\Jobs\UpdateJob->doUpdate()
#16 /.../w/extensions/SemanticMediaWiki/src/SQLStore/ByIdDataRebuildDispatcher.php(171): SMW\MediaWiki\Jobs\UpdateJob->run()
#17 /.../w/extensions/SemanticMediaWiki/src/Maintenance/DataRebuilder.php(247): SMW\SQLStore\ByIdDataRebuildDispatcher->dispatchRebuildFor(56)
#18 /.../w/extensions/SemanticMediaWiki/src/Maintenance/DataRebuilder.php(147): SMW\Maintenance\DataRebuilder->doRebuildAll()
#19 /.../w/extensions/SemanticMediaWiki/maintenance/rebuildData.php(141): SMW\Maintenance\DataRebuilder->rebuild()
#20 /.../w/maintenance/doMaintenance.php(103): SMW\Maintenance\RebuildData->execute()
#21 /.../w/extensions/SemanticMediaWiki/maintenance/rebuildData.php(174): require_once('/var/www/htdocs...')
#22 {main}The wiki is currently on MW 1.25.5, Widgets 1.2.1 and PHP 5.4.45.
@Yaron_Koren I added you as a subscriber since I figure that you may want to know about this. Probably you could even help the cause if time permits. :)