Question: Changes in Maple 2018? Getting bugs

When running this code in Maple 13 and 16 this works just fine,

GenMs:= (k::posint)-> assign(m||(1..2*k) =~ seq([dx||i, dy||i][], i= 1..k)):
GenMs(k), m || (1 .. 2*k);
gln := evalDG(l1 &s n1+`&s`(l2, n2)+sum('epsilon || i'*(cat(m, 2*i-1) &s cat(m, 2*i-1)+cat(m, 2*i) &s cat(m, 2*i)), i = 1 .. k));

But running the same code in Maple 2018 I get the following error:

Error, (in DifferentialGeometry:-Tensor:-SymmetrizeIndices) expected 1st argument to be a tensor. Received: `m2*i-1`^2

I don't know if it's related to Maple 2018 screwing with my tensor formatting:
https://gyazo.com/88eaeceda2e36cf411df44dbc4aa3ab6

(compare https://gyazo.com/b33396131165d66bbcf16e45d20cc579)

For whatever reason I just noticed that my inline &t's have been turned into `&t` but that's a separate issue.