Tin will dissolve in sulfuric acid, As tin is above hydrogen in the reactivity series, tin sulfate is soluble in sulfuric acid, and tin sulfate is soluble in water 33g/100ml @ 25deg C.
Even metals not normally reactive to an acid or base, may be attacked as an anode in an electrolyte,(or the metal atom may be oxidized, dissolved into solution after losing an electron, fron the applied electric force of the battery or power supply) the electrical current can force electrons to move in the atom of a metal that could be resistant to leave there place in the same acid, or base otherwise. (not sure I said to make it understandable).
Tin can also be electroplated in a cell , I remember reading something about shorts being caused in cells by the tin whiskers that form, (I really do not know details of plating tin or what electrolyte is used).
So it seems to me tin could build up in the sulfuric cell, if much solder was involved, I do not know if may try to plate to the lead cathode or stay dissolved in solution, or be reduced by the cathode as sludge in your cell or not.
Lead sulfate is pretty insoluble so I suspect lead from any solder would report with the gold powders.
Sorry I am not much help here,
If I was interested in learning more of what may happen, I would set up a small experiment, A small cell, concentrated sulfuric acid, small cathode of lead metal, and some 95% tin solder for the anode, run this with tin alone taking measurement's and observing what you can to see what may happen with the tin here.
I suspect like everywhere else, eliminating solder and tin before and keeping these out of a process, just helps to keep from having troubles in your process.
