Why can't I edit the 'compare at price' in my online store?

I am still in the process of setting up my store and adding product listing, collections etc. I was able to add a “sale” tag to one of the product by adding a higher “Compare at price” price.

Now, for some reason, I can no longer do it on other products, and on the one I’ve set it up previously I can’t even turn it off. The fields in settings are no longer editable.

Can someone suggest a solution?

I thought it could be linked to the Plan I am on, but this is not specified as a separate feature in any of offered plans in the Plan Comparison table (I just registered and was on 3-day trial, today I switched to Basic, and later noticed this, hence the assumption it is Plan related).