Hi deg86

When you say the entire line disappears, is this when you are adding a GST code to a Journal Entry, Invoice or Expense? Hoping to know where you are experiencing this so I can test it on my side. Typically, whenever you find your QuickBooks is giving unusual display errors or behaving abnormal it could potentially be related to the web browsers. 

QuickBooks Online uses browser cache and cookies to run faster. But there are rare times when cache and cookies cause small problems. What I would encourage you try is clear the cache and cookies before trying again, where you click here for the steps. 

Give this a go and please let us know if this is still unresolved. 

Thanks, 

-Steven