Drupal 8.x

I created a Drupal module that uses \Drupal::currentUser(); to build a list of people that have the same value for a custom field.  

The code seems to work when I run as the Administrative user.  However if I use an Authorized user it will update the values shown the first time but when I switch to a different Authorized user it still shows the same values as the first Authorized user I logged in as.  

How do I get the code to run when a new user logs in so that they see the information associated with them. 

For reference here is the code I wrote:

Hello,
I often have to replace images in Drupal8 running on Debian 9, eg. after working on them with Gimp. I do the following, which in my mind should do the trick:
- load a particular image file into Gimp (eg. the site-logo, or any other jpg/png-file.
- modify the file and then export it to the place it came from
- do a "drush cr", followed by a reload of the page that contains the supposedly modified
  image.
Afterwards the changed image should be displayed, correct? Well, it is NOT, the "old" one
still gets displayed. 

I am a first time Drupal user and am installing it (version 8) on a Windows 2016 Server using IIS. I have all the prerequisites installed and went through the Drupal installer. I entered the database info, chose 'minimal' installation, configured the site (the last step of the installer), and when it finished it gave the error, "500 internal server error".

I then reloaded the url it finished on (http://mydomain/user/1) and it loads without the 500 error.

I want to develop a Payment Gateway for Drupal Commerce 8. But I don't really understand the difference between a Payment Gateway and a Payment Method. What are the differences? What belongs where and is there any payment module available to see a good example?

Edit: I am talking about the classes

Drupal\commerce_payment\Plugin\Commerce\PaymentMethodType\PaymentMethodTypeBase 

and 

Drupal\commerce_payment\Plugin\Commerce\PaymentGateway\OnsitePaymentGatewayBase

I want to redirect a URL like https://example.com/index.html#services to https://example.com/clientsin .htaccess file in Drupal 8. Kindly help me.

I'm new to Drupal and I'm wondering if it is really true there is no way to see what's run in the CRON queue from the UI.