Without  explaining  even the meaning of “SQUID”  and the  theory behind , I make three points:

[I]This ligand is  typical in the sense that the unpaired electron is not delocalized over whole of the radical ; rather is LOCALIZED In its π^*   MO ,i.e. behaves like a “free electron” to  give only one peak( g ≈ 2 ).

.[II]  Even if any paramagnetic species obeys all the rules which are required  of  its ESR  peak/s to be observed, yet if its  minimum detectable sensitivity   is not 1010 spins/G  for X-band ESR and 1013 spins/G  in “SQUID”, it will  not show any ESR ,i.e. no peak/s are expected to be observed .

[III] This ligand does possess 1010 spins/G ( comparatively smaller number) in X-band but it  can not attain as high value as that of  1013 spins/G in “SQUD” because it is  not exposed ( spread ) over whole of the ligand; rather it is localized in π^*   MO.

 In fact, with all the merits of “SQUID” over X- band ESR, this is one of the limitation of “SQUID”. But  it happens in the rarest of the rare  cases and this ligand falls in this category. It will not be out of context to mention here that it is also typical for its one more property ---- its peak shows anisotropy

{A} It is to bring to your kind observation that I have  based my answer to this questions on the three points- why  only one peak  in this ligand, 1010  spins/G  in X-band and 1013 spins/G in “SQUD”. I , humbly, reiterate that all three facts can be well located if one surveys the literature on  ESR in general  and  this ligand in particular .

{B} Even in  my  answer to your previous question, I have cited a well established relation.

{C} Yes; I do not deny  your prerogative of agreeing/ disagreeing with my arguments. 

Thank you Sir....