So I did all 3 test missions for sprites. Then I did the selection mission. I chose Maskeraith. I got credit for the selection mission.
Then I did the Collector mission. Within 10 seconds on that board, my sprite disappeared. There is no information at all on the Sprite screen and I cannot redo the selection mission.
You probably just unequipped it by accident some how, look under the player tab where your weapons are and there should be a tab labeled battle sprites. Just click on that and click the sprite (if its there) and click equip.
I freaked out a bit at first when it happened to me only because it includes your sprite with load-outs, So you may need to remake your current load-outs to include your sprite.