You should always plot a graph when doing any solving type activity. Some of your equations have two solutions as I alluded to before. When you use find root you will get one of them and this may not be the same one excel gets. Use solve to get both. Sometimes you can also get multiple solutions if you have alternating cash flows and most introductory finance texts note this as one of the drawbacks of internal rate of return.

Solve[TimeValue[Cashflow[values[[1 ;; 7]]], r, 0] == 0, Reals]

{{r -> -1.25357}, {r -> -0.724255}}

Check both of your answers.

TimeValue[Cashflow[values[[1 ;; 6 + 1]]], r, 0] /. {r -> -1.2535683433939733`}

TimeValue[Cashflow[values[[1 ;; 6 + 1]]], r,  0] /. {r -> -0.7242552925326607`}

Plot the NPV. There are two solutions for some of the NPV curves.

NPV[i1_] := TimeValue[Cashflow[values[[1 ;; i1 + 1]]], r, 0];
curves = Map[NPV[#] &, Range[1, 6]];
Plot[curves, {r, -1.5, 0.3}, 
 PlotRange -> {{-1.5, -0.3}, {-100000000000, 100000000000}}]

All your internal rates of return are negative. Mathematically speaking, Mathematica is giving you the correct solutions. In fact it even gives you multiple solutions. Unless you are a central banker these negatives rates don't really make sense even in the current deflationary environment so you might want to constrain your solutions

Solve[TimeValue[Cashflow[values], r, 0] == 0 && r > 0, r, Reals]

If you use your first 11 cash flows you gets solutions of -144% and -51% and if you plot the present value it approaches infinity as r approaches -100%. I guess if your current holdings are to become worthless in the next period then promise of $1 at that time would sound quite attractive.

Yes - looking to calculate the rolling IRR.

Thanks for the tip on Do and Print...

Regardless of whether or not it's a good financial deal Mathematica should could up with the right answer. If you change the starting point you get different values being wrong.