Hi Marcos,
If the instance 11 was up and running, but this issue happened, you may check whether any error was reported in SM21 and ST22.
You may also check DB logs, DBSQL_NO_MORE_CONNECTION looks like a DB resource issue.
If no clue is found in SAP system, you may try to update SAP Kernel to the latest patch, and ensure the latest SUM packages is used.
Best regards,
Charles