Just for completeness, grab the .ini file, put it into the WinMFT folder along with the downloaded firmware file, and try to flash again without forcing. Let us know what happens.
I got all the files from the post. I guess I can go back and try to create my own firmware file.
PS C:\Users\Administrator.XXX> mst status
MST devices:
------------
mt26428_pci_cr0
mt26428_pciconf0
C:\Users\Administrator.XXX>flint -d mt26428_pci_cr0 query
Image type: ConnectX
FW Version: 2.10.720
Device ID: 26428
Description: Node Port1 Port2 Sys image
GUIDs: 14feb59097fee724 14feb59097fee725 14feb59097fee726 14feb59097fe
e727
MACs: 14feb5fee725 14feb5fee726
VSD:
PSID: DEL09A0000009