I have no idea if it is on your side Bungie or on Microsofts. But I have to re-download Destiny 2 entirely just for a 7GB Season Pass Update. Maybe that's a problem caused by the update, maybe it's a problem on Xbox side...
Please check for other reports on your feedback channels.
I fall back to running the game for today on PC to look up what the new Season brings. But I am not playing today because of this.
-
A full download of the game normally happens when corrupted data is found on your hard drive during the update so the system downloads everything again to try and overwrite the corruption. PCs can get away with a "scan and repair" so just need to download the relevant information again but consoles can not do this so they download everything.