@cyberspyderms can you provide some more information such as the error message that would indicate that it isn't working. Also, have you cleared the cache on the websites?

What is the component as it sounds like a problem with that. I regularly uninstall and re-install the same component without any issue

@jwaisner There is no error message given. The install icon "spins" and the upload/install page simple reloads with no success or error message provided. Yes, all site cache was cleared. We've been doing Joomla sites for about 15 years now and this is something new to us and has only appeared since the last .16 to .18 update.

@brianteeman I have uninstalled several different components/packages on different sites and also tried to install another component/packages on them. The problem occurs once a component/package is uninstalled, nothing else can be installed on that site.
True, that this was first noticed when troubleshooting a specific component (simply uninstalling and trying to reinstall a clean/new version instead of an on-site updated version)m but was not able to install anything after the uninstall. We've since verified this issue with other components/packages. Once anything is uninstalled, nothing else can be installed by normal methods, except as mentioned by URL.

I just double checked one of my sites. I uninstalled akeeba backup and then reinstalled akeeba backup with no problem at all

@brianteeman That's good to know, but doesn't solve our issue. :-) If you've got a way to get you login info securely/privately, I'll set you up, if you wouldn't mind taking a look.
We could understand this on maybe one or even two sites, but it happens on every site that we check on.

well you never said what the extension is so I couldnt check that extension

sorry but I dont look at specific sites except on a commercial basis

@cyberspyderms Please ask help in Joomla Forum. https://forum.joomla.org/viewforum.php?f=710

@brianteeman I understand about working on sites.
I did specify that we had tried several different extensions on several different sites and in the Additional Comments, I listed "problem for us that was discovered accidentally when trying to repair a bad update of SpeedCache (Joom United)" However, we tried uninstalling something different on a site that has never had that extension installed on it and was not able to install anything afterwards. Plus, on sites that don't have that extension and those that do, we are able to install like normal, until anything is uninstalled.

@Quy - I have earlier today - https://forum.joomla.org/viewtopic.php?f=708&t=979692 Just now looking at some comments there.

Set to "closed" on behalf of @jwaisner by The JTracker Application at issues.joomla.org/joomla-cms/28846

As this is related to a 3dp application and not core,closing. Please refer to the forum for assistance with 3dp issues.

This is not specifically related to a single 3dp, but happens on every Joomla site that we've checked on since the update to .18

@cyberspyderms plz send me credentials and website to harald.leithner@community.joomla.org

Tks @HLeithner for looking at this.

Thanks, Harald.
I am adding you on three sites and will email you the info about each so you can take a look.

https://www.cyberspyder.net/

From: Harald Leithner notifications@github.com
Sent: Tuesday, April 28, 2020 1:28 AM
To: joomla/joomla-cms joomla-cms@noreply.github.com
Cc: cyberspyderms info@cyberspyder.net; Mention mention@noreply.github.com
Subject: Re: [joomla/joomla-cms] Cannot install anything after uninstalling something -- AFTER 3.9.16 --> 3.9.18 upgrade (#28846)

@cyberspyderms https://github.com/cyberspyderms plz send me credentials and website to harald.leithner@community.joomla.org mailto:harald.leithner@community.joomla.org

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With the help of @HLeithner we've been able to determine this so far - in regards to this issue:
This issue seems to arise, after the 3.9.18 upgrade and seems to be only affecting installation of packages, once a package has been uninstalled. Plugins seem to be OK and not causing anything to break.
Will post more updates as we figure them out as we're communicating directly via email at this point.

I tested with akeeba backup and that is a package and there was no problem at all - so what is the package that is failing

It was mentioned in "Additional Information", a paid extension: SpeedCache by Joom United

@toivo

It was mentioned in "Additional Information", a paid extension: SpeedCache by Joom United

We have also this comment

However, we tried uninstalling something different on a site that has never had that extension installed on it and was not able to install anything afterwards. Plus, on sites that don't have that extension and those that do, we are able to install like normal, until anything is uninstalled.

I tested with akeeba backup and that is a package and there was no problem at all - so what is the package that is failing

@brianteeman - different packages as @ReLater mentioned above. In working with @HLeithner , we may have discovered that it may be related to our user account, as he is testing with us on a particular site with us (he has his own account) and is able to install/uninstall packages on the site, but we cannot install packages on the same site under our own account.
I'll keep everyone updated - stay tuned ...

To all (@brianteeman @ReLater @tolvo and especially @HLeithner )that have reached out - THANK YOU.
The root cause ended up being a corrupted file in Google Chrome on one specific PC and not any coding issues related to the update of J from .16 to 18 - even though it only appeared after the upgrade. Very strange timing indeed.

Glad you managed to solve it