RDS stuck in storage-optimization

Hello.

In rare cases, expanding RDS storage can take more than 24 hours.
There is no way to speed this up, all you can do is wait until it finishes.
I think you can connect to the database, so I think it's a good idea to wait patiently for it to complete.
https://repost.aws/knowledge-center/rds-stuck-in-storage-optimization

Typically, the storage optimization completes in a few hours, but can sometimes take up to or more than 24 hours. When the DB instance is in the storage-optimization state, the instance is operational. Your application availability isn't affected. You don't have to wait for the DB instance to be in the available state to run your applications.

Note: There's no way to speed up this process. You must wait for the optimization process to complete. The process takes longer for larger storage size increases and storage usage. Because this is an automated process, there's no fixed way to determine how long it takes to complete storage optimization on your RDS DB instance.

Could this be an issue on the AWS side?

This is difficult to judge.
The time it takes to make changes will vary depending on how you use RDS.
If it is an issue on the AWS side, you may receive a notification on the service health dashboard, etc.

As per AWS it can sometimes take more than 24hr so it is not unexpected.

If you do have AWS support raise a ticket, you can't really do anything but wait.