The following error appears when I try to save a change to an SP PageBuilder page

I upgraded from J4.4.14 (SP Page Builder 6 Pro 5.3.2) to J5.4.4 (SP Page Builder 6 Pro 6.3.2); due to the same problem and the error persists.

My homepage disappears and the following appears:

RuntimeException: 'Headers already send (output started at /var/www/html/templates/shaper_educon/sppagebuilder/addons/feature/site.php:1' thrown in /var/www/html/libraries/joomlatools/library/dispatcher/response/transport/http.php on line 56

while handling exception

Error: 'Object of class stdClass could not be converted to string' thrown in /var/www/html/templates/shaper_educon/sppagebuilder/addons/feature/site.php on line 75
Stacktrace

#0 /var/www/html/components/com_sppagebuilder/parser/addon-parser.php(1136): SppagebuilderAddonFeature->render()
#1 /var/www/html/components/com_sppagebuilder/parser/addon-parser.php(500): AddonParser::getAddonHtmlView(Object(stdClass), Object(stdClass), 'page-3731', false, Array)
#2 /var/www/html/components/com_sppagebuilder/views/page/tmpl/default.php(90): AddonParser::viewAddons(Array, 0, 'page-3731')
#3 /var/www/html/libraries/src/MVC/View/HtmlView.php(416): include('/var/www/html/c...')
#4 /var/www/html/libraries/src/MVC/View/HtmlView.php(204): Joomla\CMS\MVC\View\HtmlView->loadTemplate(NULL)
#5 /var/www/html/components/com_sppagebuilder/views/page/view.html.php(75): Joomla\CMS\MVC\View\HtmlView->display(NULL)
#6 /var/www/html/libraries/src/MVC/Controller/BaseController.php(697): SppagebuilderViewPage->display()
#7 /var/www/html/components/com_sppagebuilder/controller.php(85): Joomla\CMS\MVC\Controller\BaseController->display(true, Array)
#8 /var/www/html/libraries/src/MVC/Controller/BaseController.php(730): SppagebuilderController->display()
#9 /var/www/html/components/com_sppagebuilder/sppagebuilder.php(33): Joomla\CMS\MVC\Controller\BaseController->execute('')
#10 /var/www/html/libraries/src/Dispatcher/LegacyComponentDispatcher.php(71): require_once('/var/www/html/c...')
#11 /var/www/html/libraries/src/Dispatcher/LegacyComponentDispatcher.php(73): Joomla\CMS\Dispatcher\LegacyComponentDispatcher::Joomla\CMS\Dispatcher\{closure}('/var/www/html/c...')
#12 /var/www/html/libraries/src/Component/ComponentHelper.php(361): Joomla\CMS\Dispatcher\LegacyComponentDispatcher->dispatch()
#13 /var/www/html/libraries/src/Application/SiteApplication.php(217): Joomla\CMS\Component\ComponentHelper::renderComponent('com_sppagebuild...')
#14 /var/www/html/libraries/src/Application/SiteApplication.php(271): Joomla\CMS\Application\SiteApplication->dispatch()
#15 /var/www/html/libraries/src/Application/CMSApplication.php(304): Joomla\CMS\Application\SiteApplication->doExecute()
#16 /var/www/html/includes/app.php(58): Joomla\CMS\Application\CMSApplication->execute()
#17 /var/www/html/index.php(51): require_once('/var/www/html/i...')
#18 {main}