How a ghost variable never appear but always reported not defined

There is no variable ‘A’ applied or assigned anywhere in this function. With multiple reboost of my laptop and atom, there is still the error report:
‘A not defined’. I really cannot fight against a ghost. Do anyone know what’s happening?

PS: I traced along every function called in this execution and ensured no ‘A’ variable anywhere at all.

Solved by matching the column dimension of original D[f] with the x assigned to D[f] for updating. But the error report really swerved me to bush :cry:.

The inner-most call in the stack is in LazyArrays, and is this line, which is displaying an error message. It includes the interpolated expression $(map(x->size(x,2), A)), but A doesn’t exist. It should probably be a instead.

Probably worth a bug report to LazyArrays.