Thank you for your response and reaching out with help. I have worked around my issue by starting the project from scratch and therefore no longer need the file. I'm happy to help if the file could offer a hint to the cause of my issue and by such preventing it from occurring again.
As for the additional information:
I'm using Windows 10 20H2.
The file was worked on and saved in Affinity Publisher 1.9.0 unfortunately I don't have a record of the remaining part of release number as an updated of the program has come out since.
It was saved on local SSD, separate to the SSD which has