Your HUD has just detached after you clicked "I see it" on the blue menu.

You need to wait 15-30 secs (longer if the sim is laggy) before you re-wear, otherwise you might lose changes.

 

If you're in a hurry, there's a faster way:

1. Press ctrl-shift-1 to call up the Statistics pane.

2.  See at the bottom Pending Uploads - when you detach your HUD...that Pending Upload will go up by 1.

3.  Only re-wear your HUD AFTER it goes back down to 0.

If Pending Uploads remain at 0  for 15-30 secs or more without moving, and your sim is not laggy, it means the sim might already have updated the changes, only it happened so fast it doesn't even show on your screen. In this case, It should be safe to re-wear.