Zero value (USD) and Non Zero value (CAD) in Invoice - PK 81

Hi experts,

I have the below case - where in PK 81 has posted zero value in USD and non zero value in CAD (Local currency).

PO - Vendor currency CAD, PO currency USD. Exchange rate 1.24200

Invoice posted after 5 months with Exchange rate 1.22641. (2 GRs were posted and 3 days later this invoice posted)

Please suggest what could be the reason for this?

Regards,

Akash Prekar