How to turn off this option ?

in free version this sale / discounted price is not apearing but in full version yes, it disapear after some time or after saving customer few times.

Is there any other option to turn it off ?

there is no sales prices set for these products.

It's a individual pricing for each customer type / different than regular price but customer don't see regular price only theirs so it should show up like that 

Here is another customer loged in our and saved few times and this one have normal prices