It's a VERY common issue with GOTG. When I bought mine; the rep warned me ahead of time of all the common problems with this particular machine. He said the drop target getting stuck was, by far, the most prevalent issue. He ordered me a new one (free for me) and told me to disable the drop target in the settings until the new one came.
I disabled it in the settings; but it still ended up getting triggered during Groot multiball and messed up the rhythm of the game.
Once the new drop target assembly came; I installed it, adjusted it for height and haven't had an issue since. Hope your rep helps you out.