Not sure if there is no techi easy answer.
1. You need to use Airport Extreme in internet sharing mode not the bridge mode for the guest network to work.
2. If it worked before and you did not change anything I suggest you reset Airport Extreme, connect its WAN port to the Huawei, put yourself on WiFi or even better on the cable to Airport Extreme LAN port and rerun the Connection Wizard from Airport Utility.