Disappearing faint line??

So 8 dpo I got a super faint line on a hmt (pictured below)

I tested again this morning with fmu at 11 dpo, thinking that 48 hours would darken it a little but it looks negative...

Is there any reason this could happen? Was the first frer just an indent or something? Period due on 29th, thinking i’ll just wait to see if AF comes...