[solved itself] Installation 3.6.4 10187

[diri]

After I encountered problems with installation of AIO for version mentioned I tinkered a little bit:

Joomla 3.9.12, PHP 7.2.24

Comparing two independent systems:

One with VM 3.6.4 component installed, one without it.

Using default ISIS in Backend page extensions-> install was gone on both systems.

I found following errors in source of install page at system without VM 3.6.4 but VM 3.6.3 10184:

"PLG_INSTALLER_PACKAGEINSTALLER_UPLOAD_ERROR_UNKNOWN":"Fehler: Unbekannter Fehler oder ung\u00fcltige JSON-Ausgabe.","PLG_INSTALLER_PACKAGEINSTALLER_UPLOAD_ERROR_EMPTY":"Fehler: Der Server gibt eine leere Antwort zur\u00fcck.","COM_INSTALLER_MSG_INSTALL_ENTER_A_URL":"Bitte eine URL eingeben.","COM_INSTALLER_WEBINSTALLER_INSTALL_OBSOLETE":"Das Plugin \u201eWebkataloginstallation\u201c muss aktualisiert werden.","COM_INSTALLER_WEBINSTALLER_INSTALL_UPDATE_AVAILABLE":"Es steht eine neue Version des \u201eWebkataloginstallations\u201c-Plugins zur Verf\u00fcgung. Es wird empfohlen die Aktualisierung schnellstm\u00f6glich durchzuf\u00fchren.","JLIB_INSTALLER_UPDATE":"Aktualisierung","PLG_INSTALLER_WEBINSTALLER_CANNOT_INSTALL_EXTENSION_IN_PLUGIN":"Diese Erweiterung kann nicht \u00fcber das Webkatalog installiert werden. Bitte besuchen Sie die Website des Entwicklers um diese Erweiterung zu kaufen und zu downloaden.","PLG_INSTALLER_WEBINSTALLER_REDIRECT_TO_EXTERNAL_SITE_TO_INSTALL":"Sie werden auf folgenden Link weitergeleitet, um die Registrierung oder den Kauf abzuschlie\u00dfen: [SITEURL]"},"plg_installer_webinstaller":{"base_url":"https:\/\/appscdn.joomla.org\/webapps\/","installat_url":"aHR0cHM6Ly93d3cuendlaXJhZC1wcm9ic3QuZGUvYWRtaW5pc3RyYXRvci9pbmRleC5waHA\/b3B0aW9uPWNvbV9pbnN0YWxsZXImdmlldz1pbnN0YWxs","installfrom_url":"","product":"Sm9vbWxhIQ==","release":"My45","dev_level":"MTI=","installfromon":0,"language":"ZGUtREU=","is_hathor":0,"pv":"Mi4wLjE="}}

Changing Joomla's backend to Hathor fixed issue - install page visible and usable. VM 3.6.4 component, AIO, language files, ... installed without error.

Now, what happened at both systems before:
Both systems got an update of Akeeba Backup to Akeeba Backup Core 6.6.1 (2019-10-21).

Question is: Who is causing the problem?
a) Akeeba backup
b) VM (reading update xml is enough to switch off install page, before 3.6.4 there has been no error detected)
c) both

edit:
Switching back to ISIS after successfull installation von VM 3.6.4 manually install page is unusable again.

edit:
Testing it at 01/11/2019 08:00pm - same problem
Testing it at 02/11/2019 07:00am - problem vanished.

hm.