Several more things to note:

 

It is never a good idea to simulate for only 1/2 of a cycle, or even 1 cycle - especially when inductors are involved!  A far better thing to do is to simulate for 10s to 1000s of cycles (or more), and then apply your .MEAS commands to only the last cycle.  e.g., you might use ".tran 0 10 9.98" or similar.

 

Because you extracted their amplitudes at only one specific point in time, I strongly recommend disabling waveform compression.  With waveform compression enabled, the saved points miss the peaks entirely, and now your measurements depend on interpolation.  It's far better to use ".MEAS ... RMS" over a full cycle, instead of ".MEAS ... AT".

 

By using "AT", you also introduced errors due to phase shift.  With both resistances and inductances, there is phase shift.

 

You constructed a physically impossible magnetic circuit.  You have L1 and L6 tightly coupled, and L1 is tightly coupled to each of L2, L3, and L4.  But there is zero coupling between L6 and any of L2, L3, and L4.  That is not physically possible!  This might be why it "blows up".

 

Andy