I've noticed that the minimum amount of a song that can be looped has increased significantly since I don't really know when. I remember when I was able to select a tiniest section (even a transient or a fast note) and loop it, now it's more like a sixteenth or a 32nd note.
Why was that changed is beyond my comprehension...

The minimum loop length has been 480 ticks since at least SONAR 8.5.  There have been no recent changes to minimum loop length.  I verified in both SONAR 8.5 and SONAR Platinum Early Release [2017.01].
 
http://forum.cakewalk.com/FindPost/3503759
 
EDIT:  When looping audio, remember that the project tempo affects the resolution of the loop.  The faster the tempo, the finer the resolution of the loop.  A 480 tick loop at 120 bpm covers approx. 250ms of audio, while a loop at 240 bpm plays only 125ms of audio.
 
Hope that helps,
-- Ron

Thanks for the info. I'm most familiar with Sonar 6, it was way shorter than 480 ticks in that version.
Yet another functionality has been crippled for some strange reason... oh well.

Two more questions so:
1) Is there any way to take the loop length limit off?
2) What's the point of limiting it? What's the benefit?
 
The more I think about it the more enraged I become... rant warning.
I think it is absolutely ridiculous that a DAW cannot play a short note in a loop. It's simply beyond belief that such a basic operation is impossible. It actually makes Sonar almost useless to me.
 
Let's say that I'm trying to dissect a bass line of somebody else. I import the file, connect my bass. There's a note I cannot hear properly because it's muddy/quiet/covered by different instruments or I simply don't have enough talent to figure out what the note is. In Sonar 6 I would simply loop it and try to find it on the fretboard. I can't do it now, because Cakewalk have decided to limit the minimum loop length. I can loop a note and a half or two notes which makes the whole process a lot harder.
 
Looks like I'll have to buy SoundForge, their user interface makes look Sonar like a kid toy.

 Temporarily mute the region of the looped segment you don't want to hear by dragging in the lower half of the clip with the mute tool. You'll probably be able to hear it better if it's not repeating 15-20 times a second. Then drag in the upper half to unmute it again.
 
Edited because my original suggestion to use Isolate was wrong.