The following is the April 22, 2019 Congressional Budget Office report, Costs of Submarine Maintenance at Public and Private Shipyards.
From the report
Public shipyards conduct a large majority of all submarine maintenance. Those shipyards are Navy-owned and -operated, but the Navy has been experiencing long delays—sometimes as much as several years—to obtain maintenance on its submarines at those shipyards. As a result, some submarines have missed deployments or had shortened deployments. The...
https://news.usni.org/2019/04/23/cbo-report-on-navy-submarine-maintenance-costs