Drupal 8.x

I am preparing to migrate an existing D7 site to D8.

The site is primarily used by screen reader users, so accessibility and enhancing the user experience for screen readers is a priority.

My suspicion is that many of my site users will be confused by the significant change made to the node preview page in D8 (bearing in mind that they have no visual cues, so rely solely on the screen reader to know what's on the page).

When I try to run cron from the Drupal UI (Configuration > Cron) I get an 'unexpected error' message.

Looking into my Recent Log Messages, I see this error:
"Symfony\Component\Routing\Exception\InvalidParameterException: Parameter "key" for route "system.cron" must match "[^/]++" ("" given) to generate a corresponding URL. in Drupal\Core\Routing\UrlGenerator->doGenerate() (line 204 of [mywebsite]/public_html/core/lib/Drupal/Core/Routing/UrlGenerator.php)."

After upgrading to Drupal 8.9 or 9.0 all my custom modules always give the last result as if it's fully cached. I'm logged in as the admin user. On another web browser I get the same cached result.

I quickly wrote a simple module that shows the GET variables, a random number and the first line of a text file.

Each time I start it I get the same output. If I clear all caches in /admin/config/development/performance, I get one time the correct new data.

Until Drupal 8.8.6 all worked fine.

Tested with:

My images were broken and I had no idea what I did to make it this way. I figured I download a module or theme that messed up my abilty to upload images. So I deleted a couple mods but I didn't uninstall from administration profile I did it straight from my file manager. When I tried to run an update it said the files were still registered in drupal but the content was not there. The biggest messup was deleting a module called components from my file manager/sql. Now when I try to log into my site it says The website encountered an unexpected error. Please try again later.

Is anyone using Fail2Ban for Drupal? I am getting slammed by bots and even though honeypot and captcha are doing the job of stopping and logging, I would like to take the next step and automate banning.

Fail2Ban has worked wonders for me parsing bad actors found in postfix's mail.log and banning the offenders, so I want to apply the same tactic by parsing bad actors found in Drupal's Syslog and banning these offenders as well. 

If you are already using Fail2Ban for Drupal, please post your regular expressions. I just turned on Syslog so I am a little behind the curve.

As the commenter below stated, I was running composer in the wrong folder. *SMH* I assumed it was correct because of the composer.json/lock files. That was my mistake. I'll remove those files now. Thanks!

Original post:

I have my drupal 8 site up and running, and when I put the site up I used composer require to install a list of modules. It worked great. Now, I'm trying to do the same for a few new modules and it won't work. I'm trouble-shooting and would love any trouble-shooting ideas you have. Thank you in advance!