Please upgrade to Admin Tools 6.0.3. Your version is out of date. Upgrading will also fix your problem, as long as Joomla's extensions updater works correctly this time (you'll see what I mean later on).
The problem may persist, because it is caused by a bug in Joomla's extension updater itself. If this happens please download Akeeba FEF from https://www.akeeba.com/download/fef/2-0-1.html and install it on your site twice in a row, without trying to uninstall it before or in between.
As to why it happens.
You have hit a bug in the Joomla Extensions Updater. We are forced to use the Joomla Extensions Updater and let it handle the updates to our software on pain of our software being removed from the Joomla Extensions Directory, something which would have an adverse impact to our business. The Joomla Extensions Updater has a lot of known bugs we have been privately reporting to the Joomla project since 2014. They did not address them, they did not let us contribute fixes to them and they still pretend they never heard about them. When we filed a public ticket on March 6th, 2021 about these issues we were met with active hostility and threats against our company. As a result we are now choosing to share this information with our clients instead of trying to cover for the failings of the Joomla project itself.
The bug you have been affected by means that Joomla fails to copy all of the files included in an update package when it's installing the update, either through the Updates page or using the Upload and Install or Install from URL features. You need to install the update package twice for Joomla to finally copy all of the files. We are trying to address it programmatically with the post-installation script we are allowed to run during the installation of an updated package. This works most of the time but not all of the time, presumably because the Joomla bug lies deep in its Files API which handles copying files across directories.
Regarding the post text and attachments. What goes unsaid in the message, for economy of space, is that an HTML file should be placed in a ZIP file before attaching it. As you can see below the attachment area we do not accept HTML files to be uploaded. This and the fact that we do not allow you to paste the entire HTML contents is for security and privacy reasons.
Regarding your attachment, it is only visible by our support staff and yourself. It is not visible to anyone else. Try logging out of our site and visit this ticket. You will see that you can no longer download the attachment. This is another privacy measure we take with regards to attachments since your attachments are far more than likely to contain privileged information about your server.
There is no need for derision and tension. We are here to help you. If you have questions or concerns we will be happy to hold a discussion about them in a professional tone.
Have a great day!
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!