We're so sorry for the delay in response. I was unable to reproduce this on our end, so could you please share a few more details like:
We're here to help, just need more info.
It's been a while we haven't heard back from you. Would you mind telling us if the issue is resolved? Please let us know if you need more assistance from us. I would also request you to please check out this article: https://helpx.adobe.com/xd/help/work-with-components-xd.html
Hope it helps.
I got the same thing going on. XD on MacOS, place a component inside another component and the component inside the component becomes locked an uneditable.