Product Description Font Size and Font type is wrong on one product

[Jack10]

Hello,

I have 4 products on my Shopify website and 3 of them have the same font and font-size in their product description but one of them does not. 

Please can you help me fix this? I can't work out why this is. 

I have shared the first photo with the wrong font and font-size and the second with the correct font and font-size