Greetings,
When I run the following code through Cadabra
{a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s#}::Indices.
eqtn := A^{f} A^{m} B_{g f} G^{a}_{m e} G^{e}_{b d}.
substitute (eqtn,$A^{e} B_{c e} G^{a}_{b d} -> A^{f} B_{f} R^{a}_{b c d}$);
it reports an exception: Triple index m inside a single factor found.
A triple m-index seems odd as there are only two m-indices in the expression (maybe an extra m-index pops up during the substitute).
This same code runs without error in Cadabra 1.16 and 1.41.
Cheers,
Leo