Disappearing lines?

According to my apps, I’m 8dpo which I know is very early but decided to test because of severe nausea and frequent urination. Yesterday and today I had very faint lines show up within 30secs-1min and would remain visible for about 20 minutes before they just disappear. They are blue dyes (I know, unreliable) and I won’t be able to buy a pink dye test until tomorrow. Anyone else experience this? I know evap lines are common but is it normal for them to disappear?