Ah, I see what’s happening here.
Bit surprised the forum used that terminology; it’s a little misleading.
So, to clarify, there are three things that can happen;
- A thread can be locked (no further replies can be posted).
- A post can be locked (no further edits can be submitted).
- A post can become too old to be edited further.
In this instance it’s the third - it’s not that this particular post has been unlocked and can be individually unlocked, but rather that the site-wide setting no longer permits edits due to how long ago the post was created. I’ll need to speak with the team about this.