Over the last several days I have received this error 503 after performing a OSU. Sometimes 'update now' from the account resolves it.
I decided yesterday to try many troubleshooting step including multiple hours with multiple online chat people who could not help resolve it.
Some of those steps included deactivating and reactivating online services, delelting the account numbers and names of the account in the details and having me change my bank password and trying a test copied template file. They said they escalated it. Later in the day yesterday it surpsingingly resolved but it's back this morning.
Evidently there is a connectivity issue between HSBC Bank USA and Quicken which needs to be fixed.