Step 1. Go to your back office > preferences > Advanced settings > scroll down to ‘appearance of columns’ section > find ‘index’ meta row > click on left column cross icon > you will now see a green tick
Step 2. You need to check that the ‘Categories Block’ is in the ‘displayLeftColumn’ hook and that the ‘index’ page is not in exemptions list. From back office go to Modules > Positions > search for ‘displayLeftColumn’ > edit
Step 3. Remove ‘index’ from exemptions list. Refer to screenshot below: