Some Instances cannot be found on one SQL Server

[zjuka]

Hello,

I have an issue when SQL Server with 10+ instances shows 7/10 and cannot find other 3. Why this can happen, where I need to dig?

Example of error:
Unable to fetch from SQL: Error opening connection to master at SQL1\NI8, timeout out at 5,000 ms @ at StackExchange.Opserver.Helpers.Connection.<GetOpenAsync>d__1.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.ConfiguredTaskAwaitable1.ConfiguredTaskAwaiter.GetResult()`