I know now it makes no difference complaining about a Sonar bug, but I still write to see if anyone else has managed to resolve this on their own.
What happens is when I insert more than 5 output channels in a single instance of Kontakt, from the SIXTH channel, Sonar shows the channel names incorrectly.
Currently I use Kontakt version 5.6.5.
 
To be clearer, I'll put the steps here so that you can simulate and see if the same happens.

1. Insert 1 instance of Kontakt with these parameters:
   
2. Within Kontakt, insert, for example, more 8 channels, after St.1:
   
3. This should be the initial result:
   
4. To make it easier to understand, I will rename each channel with the name of an instrument, with a sequential number at the beginning to indicate the original channel number:
   
5. Back to Sonar, now I'm going to reassign the first synth output originally created, to one of the other 8 new outputs I've created within Kontakt:
   
6. And here's the problem:
   
   
   

As you can see, for each instrument, 3 channels are created: 2 mono (left and right) and 1 stereo, a combination of the two previous mono channels.
Note that the names follow well until channel 5 (trumpet). But from channel 6 (flute), Sonar begins to mess things up.
In fact, this is just an incorrect writing problem.
If I ignore the wrong names, and continue marking the instruments, they will sound in the channels properly. For example, if I want to sign the tuba to its correct stereo channel, I should attach it to the "kt.8-violin / kt.9-cello: Stereo" channel.
 
Would anyone know if there is any way to solve this?

Screenshot #4 shows that aux 1, aux 2, and aux 3 in Kontakt are assigned to the same channels (11/12, 13/14, 15/16) as flute, tuba, and violin.
Setting the channel assignments for all the aux channels to not conflict with the instrument channels should fix your problem.
 
Hope this helps,
-- Ron

SquireBum
Screenshot #4 shows that aux 1, aux 2, and aux 3 in Kontakt are assigned to the same channels (11/12, 13/14, 15/16) as flute, tuba, and violin.
Setting the channel assignments for all the aux channels to not conflict with the instrument channels should fix your problem.

I made these assignments, but nothing has changed. Did you do the same test?

Results from test running Kontakt 5.7.1:
 
#1 Kontakt Output:

 
#2 SONAR Track Input List:

 
SONAR seems to be operating correctly on my system.
 
Sorry I couldn't help.  Hopefully, someone else may have some additional suggestions for your problem.
 
-- Ron

Since we both have the same version of Sonar, I conclude that the problem is in my version of Kontakt (5.6.5).
Thank you very much.