You are apparently the only person with this problem (no one else ever reported an issue in 8 years or so that the radar has been implemented)...
Of course, only the rezzed avatars can be focused (but the focus button is greyed out when they are not) and the avatar must not be in a different parcel with the "no see" flag set (and your own parcel must not be "no see" to be able to focus/see avatars in another parcel)...
Sometimes, there are also glitches with the sim servers not sending the right avatar position (these avatars appear with an altitude of 0): it's however not a viewer issue (this bug is known to LL and was indeed identified as a server "interest list" bug).
Sometimes you might also need to hit the Focus button twice for accurate focusing, because the avatar has moved, or its position was only the coarse position sent by default by the neighbouring sims as long as your camera is not pointing into them (the exact position is then sent after the first focus action and used by the second one).
If you do not like the Cool VL Viewer, please feel free to use any other viewer fancying you !
The Cool VL Viewer was created for myself (because I could not accept the disastrous UI changes and the bugs in LL's viewer). I'm sharing it for like-minded people to enjoy it. People who are not like-minded most probably dislike some features in it (or absence thereof), but it's of no concern whatsoever to me...
Clearly, you are not providing any useful info for me to identify the root of your issue. If you think there is a bug, please fill-in a proper bug report, providing the required info (in this case, exact reproduction steps would be needed, i.e. listing each and every action you do, and where (sim/parcel) and in which context (avatars in parcel or out, in region or out ? Draw distance ?). Please follow
the bug report forum rules.