In version 6.5 Microchip MiWi software and all previous versions including legacy products, the stack is validating only two out of four Message Integrity Check (MIC) bytes.
https://www.microchip.com/product-change-notifications/#/
https://www.microchip.com/en-us/products/wireless-connectivity/sub-ghz/miwi-protocol
https://ww1.microchip.com/downloads/en/DeviceDoc/asf-release-notes-3.51.0.101-readme.pdf
https://ww1.microchip.com/downloads/en/DeviceDoc/asf-release-notes-3.50.0.100-readme.pdf