Did you happen to infuse something that required level 21+ into level 20 gear? If you do that it unequips the item you infused into until you are whatever level the item infused required. Basically if you infused level 21 gear into level 20 gear the level 20 gear becomes level 21.

You need to be at least level 21 to have anything higher than power level 305 equipped. Your gauntlets are 307. Since you are level 20, those gauntlets contribute 0 to your power level, thus the drop in your power level.