I have no idea what the original problem was, however breaking it out into two different plot statements (that I originally did to see if that would help isolate the error) solved it.
x1 = 1:10;
y1 = rand(1,10);
x2 = 11:20;
y2 = rand(1,10);
figure
loglog(x1,y1,'-bo','MarkerFaceColor',[0 0.4470 0.7410],'MarkerEdgeColor',[0 0.4470 0.7410])
hold on
loglog(x2,y2,'-ro','MarkerFaceColor',[0.8500 0.3250 0.0980],'MarkerEdgeColor',[0.8500 0.3250 0.0980])
hold off
grid
The second loglog call can also simply be plot, with the same arguments.
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