The flare is the only way to find guardian location ?
In my last guardian someone of my group ping the location of the guardian at the beginning of the guardian (without flare) and after each teleport he find the new location each times.
New hack or i miss something in the game ? 
hack
Depends if it is the sand area. If you go really close to the zipline and zoom in all the way you can see 3 of 6 guardian spawn locations
Just noticed you said they pinged after they teleported. Yeah thats a hack
Here is a reddit post showing top left of woeful drylands for deskuluda
oh nice
it was with Yoho