This happened when I didn’t have discourse, and I remember the event now. I was replaying a level because my friend was stuck on it, and then when I equipped something(I think it was quartz sense stone), I equipped the deflector-for free (BTW I did not have enough gems to buy it, if you were wondering)!!!I freaked out and exited, and when I went on the armory section again, it was gone…
EDIT: Please report to the GitHub Issue-Tracker if possible!
Sadly this alone is not very helpful. Can you remember which level it was? If yes, try to play it again and see if you have the deflector equipped. DO NOT CHANGE YOUR EQUIPMENT! If you see that it is equipped, post your username and the level-name here.
If you bought the Deflector in the meantime there is little that can be done to investigate the bug I fear.
If you remember when (Date) you played the level and when you bought the deflector it might still be able. In this case provide that information as well.