I have posted about this back in December, and had some communication from Ubisoft. However, there has still not been any form of resolution to this issue, other than to suggest starting the game right from the beginning, or from a previous save.
I have made a YouTube vide which shows this issue here
As this is being played on XBox we have been advised that we cannot send over our game data to be looked at. My main query if there is nothing that can be done, is anything still being looked at to rectify this, as it has never appeared on the megathread as being looked at, and has not been resolved after numerous updates.
As a further suggestion, I am aware that AC hasn't had the option to restart missions since Origins, but based on the amount of niggly issues people clearly have with missions, would it not be the easiest fix to write this option into the code? It would then fix a huge amount of issues that people have, or at least give people the option to try it again to see if glitches get fixed before posting on this forum for help.