If anyone else ends up here I’ll add the solution:
You need to log back into your Arlo account and under “Grant Access” where you added a Home Assistant “friend” you need to add the new cameras to what you originally have shared with them then save.
If you didn’t set up a new Home Assistant profile then it’s a different problem but this worked for me!
Had a similar issue when changing base stations, and when renaming cameras. Arlo doesn’t seem to properly update all the “Friends” you’ve shared them with, unless you manually uncheck, save, then recheck the shared devices for each friend. It’s not an HA issue.