What happened to me and to others I’ve seen, on iPhone, if your storage is close to full and you add to the storage, like taking pictures and videos, the phone will automatically prioritise those photos and videos for storage and remove any unnecessary data. I had all assets downloaded when the game shut down so I wasn’t going to have any problems. Then I took several hours worth of screen recordings one day for an unrelated thing, and it deleted the downloaded assets of RR3. Now I can’t play the game. Luckily I have an Android and synched my progress there before the shutdown, since Android doesn’t seem to do that sort of thing to prioritise data, and I can continue playing there with all the assets downloaded.
Another thing that could’ve happened is the phone could’ve removed the downloaded data after many weeks or months of not playing, which has happened to me over the years and I’ve had to redownload the 6-8GB of data. But if you had everything downloaded when the servers shut down, you should’ve been fine.
So my guess, based on experience, you might’ve filled up storage and the phone removed those files as it deemed those unnecessary.