Why does Install4j fail to parse updates.xml file with SAXParseException?

Question

I am new to install4j and stackoverflow, so appologies if my qustion is not structured properly.

We are using install4j version 6.1.2 (build 6275). When our application is launched, install4j auto update receives the following error when it checks for updates, and the update is not performed (application launches with old version):

[ERROR] com.install4j.runtime.beans.actions.update.CheckForUpdateAction [ID 322]: could not download file
        java.io.IOException
java.io.IOException
        at com.install4j.runtime.installer.helper.XmlHelper.createIoException(XmlHelper.java:307)
        at com.install4j.runtime.installer.helper.XmlHelper.parse(XmlHelper.java:90)
        at com.install4j.runtime.installer.helper.XmlHelper.parseFile(XmlHelper.java:44)
        at com.install4j.runtime.installer.helper.XmlHelper.parseFile(XmlHelper.java:40)
        at com.install4j.runtime.installer.config.update.UpdateDescriptorImpl.read(UpdateDescriptorImpl.java:73)
        at com.install4j.runtime.beans.actions.update.CheckForUpdateAction.execute(CheckForUpdateAction.java:38)
        at com.install4j.runtime.beans.actions.SystemInstallOrUninstallAction.install(SystemInstallOrUninstallAction.java:29)
        at com.install4j.runtime.installer.ContextImpl$7.executeAction(ContextImpl.java:1668)
        at com.install4j.runtime.installer.ContextImpl$7.fetchValue(ContextImpl.java:1659)
        at com.install4j.runtime.installer.ContextImpl$7.fetchValue(ContextImpl.java:1656)
        at com.install4j.runtime.installer.helper.comm.actions.FetchObjectAction.execute(FetchObjectAction.java:14)
        at com.install4j.runtime.installer.helper.comm.HelperCommunication.executeActionDirect(HelperCommunication.java:272)
        at com.install4j.runtime.installer.helper.comm.HelperCommunication.executeActionInt(HelperCommunication.java:247)
        at com.install4j.runtime.installer.helper.comm.HelperCommunication.executeActionChecked(HelperCommunication.java:185)
        at com.install4j.runtime.installer.helper.comm.HelperCommunication.fetchObjectChecked(HelperCommunication.java:168)
        at com.install4j.runtime.installer.ContextImpl.performActionIntStatic(ContextImpl.java:1656)
        at com.install4j.runtime.installer.InstallerContextImpl.performActionInt(InstallerContextImpl.java:151)
        at com.install4j.runtime.installer.ContextImpl.performAction(ContextImpl.java:1103)
        at com.install4j.runtime.installer.controller.Controller.executeAction(Controller.java:367)
        at com.install4j.runtime.installer.controller.Controller.executeActions(Controller.java:333)
        at com.install4j.runtime.installer.controller.Controller.handleCommand(Controller.java:194)
        at com.install4j.runtime.installer.controller.Controller.start(Controller.java:94)
        at com.install4j.runtime.installer.Application.runApplication(Application.java:71)
        at com.install4j.runtime.installer.Application.runApplicationInProcess(Application.java:52)
        at com.install4j.runtime.installer.helper.apiimpl.ApplicationLauncherImpl$1.run(ApplicationLauncherImpl.java:39)
        at com.install4j.runtime.installer.helper.apiimpl.ApplicationLauncherImpl.launchApplicationInProcess(ApplicationLauncherImpl.java:46)
        at com.install4j.api.launcher.ApplicationLauncher.launchApplicationInProcess(ApplicationLauncher.java:58)
        at com.install4j.runtime.launcher.LauncherIntegration$2.run(LauncherIntegration.java:110)
        at com.install4j.runtime.launcher.LauncherIntegration.processLauncherIntegration(LauncherIntegration.java:114)
        at com.install4j.runtime.launcher.LauncherIntegration.processLauncherIntegrations(LauncherIntegration.java:58)
        at com.install4j.runtime.launcher.LauncherIntegration.processLauncherIntegrations(LauncherIntegration.java:51)
        at com.install4j.runtime.launcher.LauncherIntegration.checkIntegrations(LauncherIntegration.java:38)
        at com.install4j.runtime.launcher.WinLauncher.main(WinLauncher.java:25)
Caused by: org.xml.sax.SAXParseException; systemId: file:/C:/Users/.../AppData/Local/Temp/i4jupd5100269909742792694.xml; lineNumber: 1; columnNumber: 50; White spaces are required between publicId and systemId.
        at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(Unknown Source)
        at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(Unknown Source)
        at com.install4j.runtime.installer.helper.XmlHelper.parse(XmlHelper.java:88)
        ... 31 more
        Execute action not successful after 61 ms
[INFO] com.install4j.runtime.beans.screens.CustomizableProgressScreen [ID 320]: Canceled

Our updates.xml file begins with the following line:

<?xml version="1.0" encoding="UTF-8"?>

We have multiple deployment environments that use the same install4j version for the same application, but use different deployment destinations and version numbers. The auto updates are working properly in most of these environments and the updates.xml files in those environments start with the same line as the environment that is having this problem.

I didn't think it was related, but just in case, the environments that are working properly use internally hosted sites. The environment that is failing is an AWS hosted site.

Edit:

The file listed in the log does not exist. But it appears that other attempts have left behind i4jupd*.xml files, each of which are HTML format indicating the updates.xml file was moved "here"

<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>302 Found</title>
</head><body>
<h1>Found</h1>
<p>The document has moved <a href="https://.../updates.xml">here</a>.</p>
</body></html>

Thanks for your time!