Hi Paul,

I have not looked at the code in the attached notebook, however, this works fine.

ResourceFunction["CombinePlots"][
 Plot[Sin[x], {x, 0, 2 \[Pi]}, 
  PlotLegends -> 
   Placed[LineLegend[{Red, Blue}, {"Sin[x]", "Cos[x]"}, 
     LegendFunction -> (Framed[#, FrameMargins -> -2, 
         FrameStyle -> Directive[Black]] &), LegendLayout -> "Row",
     LegendMarkerSize -> {{8, 8}},
     LabelStyle -> {FontSize -> 10}], {Right, Bottom}], 
  PlotStyle -> Blue],
 Plot[Cos[x], {x, 0, 2 \[Pi]}, PlotStyle -> Red],
 Frame -> True]