I'm having the same issue on my site. In case it helps, here's a stack trace out of the everything log.
I've occasionally found weird errors that seem to stem from this being a site that I've continually upgraded from back in the J1.5 days. Every once in a while some old php file is sitting around that mucks things up. Not sure if that is in any way relevant to this issue, but thought I'd mention it just in case.
Code:
024-09-09T14:55:57+00:00 INFO 108.7.186.179 updater Loading information from update site #13 with name "Joomla! Update Component" and URL https://update.joomla.org/core/extensions/com_joomlaupdate.xml took 0.09 seconds2024-09-09T14:56:00+00:00 CRITICAL 108.7.186.179 error Uncaught Throwable of type Error thrown with message "Attempt to assign property "html" on null". Stack trace: #0 [internal function]: Joomla\CMS\Updater\Update->_startElement(Object(XMLParser), 'html', Array)#1 [ROOT]/libraries/src/Updater/Update.php(526): xml_parse(Object(XMLParser), '<!DOCTYPE html>...')#2 [ROOT]/administrator/components/com_joomlaupdate/src/Model/UpdateModel.php(1658): Joomla\CMS\Updater\Update->loadFromXml('https://joomla....', 4)#3 [ROOT]/administrator/components/com_joomlaupdate/src/Model/UpdateModel.php(1529): Joomla\Component\Joomlaupdate\Administrator\Model\UpdateModel->checkCompatibility('https://joomla....', '5.1.4')#4 [ROOT]/administrator/components/com_joomlaupdate/src/Controller/UpdateController.php(591): Joomla\Component\Joomlaupdate\Administrator\Model\UpdateModel->fetchCompatibility('10137', '5.1.4')#5 [ROOT]/libraries/src/MVC/Controller/BaseController.php(693): Joomla\Component\Joomlaupdate\Administrator\Controller\UpdateController->batchextensioncompatibility()#6 [ROOT]/libraries/src/Dispatcher/ComponentDispatcher.php(143): Joomla\CMS\MVC\Controller\BaseController->execute('batchextensionc...')#7 [ROOT]/libraries/src/Component/ComponentHelper.php(361): Joomla\CMS\Dispatcher\ComponentDispatcher->dispatch()#8 [ROOT]/libraries/src/Application/AdministratorApplication.php(143): Joomla\CMS\Component\ComponentHelper::renderComponent('com_joomlaupdat...')#9 [ROOT]/libraries/src/Application/AdministratorApplication.php(186): Joomla\CMS\Application\AdministratorApplication->dispatch()#10 [ROOT]/libraries/src/Application/CMSApplication.php(293): Joomla\CMS\Application\AdministratorApplication->doExecute()#11 [ROOT]/administrator/includes/app.php(61): Joomla\CMS\Application\CMSApplication->execute()#12 [ROOT]/administrator/index.php(32): require_once('/PATH/TO/ROOT/HIDDEN/...')#13 {main}Statistics: Posted by jhalex — Mon Sep 09, 2024 3:04 pm