Greetings docsgp,
The EOS camera will select the appropriate ISO value when metering if the camera is set to Auto ISO. This will allow for the camera to shoot at a specific ISO value and you may see the ISO change for the shot taken. When the camera is not metering and not in use, it should display that it's in Auto ISO.
If you're seeing that the camera is taken out of Auto ISO to a fixed ISO value, even after you're done taking pictures, then let's check to see if the camera is set to one of the custom shooting modes like C1, C2, or C3. It may be where an ISO value has been manually set and saved in one of the custom shooting modes. You may also clear the camera settings to restore them to factory default to see if this helps resolve the issue. You may click on the following link to follow steps on resetting the camera.
https://cam.start.canon/en/C004/manual/html/UG-07_Set-up_0290.html
If the issue persists, then you may send the camera to our facility for service.
Canon U.S.A., Inc. has created a new online repair portal that allows you to set up service in a few simple steps. The repair portal gives you the ability to set up service for multiple pieces of equipment at once, and to receive a repair estimate in the majority of cases, depending on your model and issue. The portal also allows you to upload images or videos that will assist us in repairing your product. You can also select how you wish to be notified of the progress of your repair. The portal's service history section allows you to view all services that have been performed on any of your camera or video products since January 7, 2020.
Please follow the link below to access our online repair portal to arrange for service:
https://mycanon.usa.canon.com/signin
Instructions for Accessing and Using the Online Repair Portal.
You will need to access or create your My Canon Account.
If you already have a My Canon Account and your product is already registered, simply click on the “Get Repair Services” link on the left menu and follow the onscreen instructions to arrange for service for your product.
If you have a My Canon Account and your product is not registered, you must register your product first. Click on the “Get Repair Services” link on the left menu, then click on the “Register Product” link on the right. After your product is registered, click on the “Get Repair Service” link on the left menu and follow the onscreen instructions to arrange for service for your product.
If you do not have a My Canon Account, you will need to create one. After you create your account, click on the “Add Product” link to register your first product. After your product is registered, click on the “Get Repair Service” link on the left menu and follow the onscreen instructions to arrange for service for your product.
Once you have completed the repair request, you will have an opportunity to print a copy of the request for your records. This request form will also contain shipping instructions and an address label that you will attach to the outside of your shipping box when mailing your equipment for repair.
