Xiao Ai, a student of Mi band 5, suggested that the reason for the loss of authorization was that Xiao Ai was not authorized in Xiaomi Campaign, so everyone authorized Xiao Ai to use it through Xiaomi Campaign.
After turning on Xiaomi Sport on your mobile phone, click My in the lower right corner of the interface, select the mi band 5 device among my devices, and click Enter. Slide the screen up, find and click Xiao Ai. Then click below to authorize, and then click to authorize successfully.