Question: Incorrect use of independent variables (PDE)

restart:
with(PDEtools):with(plots):
declare(u(x,y,t)):
PDE1:=diff(u(x,y,t),t$1)+a*u(x,y,t)*diff(u(x,y,t),x$1)+diff(u(x,y,t),x$3)+

b*diff(u(x,y,t),y$2)=0;
Sol1:=pdsolve(PDE1);

Test1:=pdetest(Sol1,PDE1);

params:={a=6,b=1,_C1=1,_C2=1,_C3=1,_C4=1};

Sol2:=subs(params,Sol1);

plot3d(subs(t=1,rhs(Sol2)),x=-10..10,y=-10..10,axes=boxed,grid=[50,50],

style=patchnogrid,shading=Z,orientation=[-40,50]);

Sol3:=[SimilaritySolutions(PDE1,removeredundant=true)];

Error, (in PDEtools:-ToJet) incorrect use of independent variables {_phi} in 

the names of the  dependent variables {_phi[3](_phi[1], _phi[2])}

Test2:=map(pdetest,Sol3,PDE1);

Error, (in pdetest) unable to determine the indeterminate function

Sol4:=combine(subs(params,Sol3));

                      
plot3d(subs(t=1,rhs(Sol4[3])),x=-10..10,y=-10..10,axes=boxed,grid=[50,50],

style=patchnogrid,shading=Z,orientation=[-40,50]);

Error, invalid input: rhs received Sol3[3], which is not valid for its 1st argument,

 expr

Thanks