Off-hand slot not working

At some time point in 4-21th, my shield in my first off-hand slot suddently became unavailable. The shield was surely equiped in the slot, the shield icon was in my first off-hand slot too, but in game it did not work and no icon of off-hand shield showing in left-down UI as well as my parry was done like without shield.

I can only put my weapon and shield in the 2nd main-hand and off-hand slots and everything works.