In previous post of HSRP, a problem has highlighted of reverse and forwarding traffic when customer use the HSRP in LAN. This post is highlighting the problems when HSRP runs in PE-CE wan. Below is the diagram shown for reference purpose.

Customer R6 is connected with two PE routers for high availability. R3 is the active router with priority 255 and R2 is the standby router with priority 200. R1 ie receiving the lan routes from R2 as well as from R3 but selecting R2 as the best path because of smallest router-id assuming the cost of the both links in cloud is same. So the forwarding from R6 is happening via R3 router and reverse traffic is coming via R2.
Which Problems Could Come
1.The different reverse and forwarding could cause problems ofin customers applications if applications are jitter or latency senstive.
2. If the primary and backup path has different bandwidth allocation, In that case backup could be obstructed at anytime.