It could be a breadcrumb quest from another zone leading to STV or a quest chain that started in an earlier zone that you’re missing.
It’s easily fied.
You can right click the pickup quest in the tracker to open the Guide window. Find the quest not available and double tick until there’s a read X in the box. It’ll then skip the quest+pre/follow ups. and the guide should point you to the next doable quest.
This is also how you skip a quest you don’t want to do (Example: Hogger).