Hello.Is this a mistake or something else? Can you help with this issue?

Exception thrown when sending notification: System.Threading.Tasks.TaskCanceledException: A task was canceled.
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x00026] in <437ba245d8404784b9fbab9b439ac908>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x00028] in <437ba245d8404784b9fbab9b439ac908>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x00008] in <437ba245d8404784b9fbab9b439ac908>:0 
  at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in <437ba245d8404784b9fbab9b439ac908>:0 
  at System.Net.Http.HttpClientHandler+d__64.MoveNext () [0x004f5] in <7ebf3529ba0e4558a5fa1bc982aa8605>:0 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <437ba245d8404784b9fbab9b439ac908>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0001a] in <437ba245d8404784b9fbab9b439ac908>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x00028] in <437ba245d8404784b9fbab9b439ac908>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x00008] in <437ba245d8404784b9fbab9b439ac908>:0 
  at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter[TResult].GetResult () [0x00000] in <437ba245d8404784b9fbab9b439ac908>:0 
  at System.Net.Http.HttpClient+d__47.MoveNext () [0x000ca] in <7ebf3529ba0e4558a5fa1bc982aa8605>:0 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <437ba245d8404784b9fbab9b439ac908>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0001a] in <437ba245d8404784b9fbab9b439ac908>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x00028] in <437ba245d8404784b9fbab9b439ac908>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x00008] in <437ba245d8404784b9fbab9b439ac908>:0 
  at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in <437ba245d8404784b9fbab9b439ac908>:0 
  at CompanionServer.NotificationList+d__13.MoveNext () [0x00176] in <2dfe8a113bba444f8870d870e197b13c>:0 

The error is with Rust's Rust+ companion app support. You'd need to report it to Facepunch.

How exactly and from where do I report?

https://rust.facepunch.com/ > Support