I’d say that SDPT3 is not very robust. SeDuMi handled this o.k.
The following was found to be feasible with SDPT3: There is indeed a solution slack = zeros(9,1) and x = A\b, as there must be because A is non-singular.
cvx_begin
variable x(9)
variable slack(9) nonnegative
minimize (norm(slack))
subject to
A*x + slack == b
cvx_end