Hello,
There’s currently a few bugs with the attach tracks. First is that when you move an objects that is attached through an attach track, it doesn’t set relative transformation keyframes. That’s most likely what you’re seeing. We’re looking to fix this in an upcoming release. Unfortuantely for now, the only thing you can do is to set values directly through the details panel or the value editors in Sequencer. Another bug is that when you move the parent object, the child object doesn’t immediately update to it’s new position. It only moves when you scrub. The internal jira items for tracking these issues is UE-30373.