Does big current draw make GFCI outlets go bad?
I have noticed that GFCIs seem to be worn out by heavy, prolonged loads.  I can't find any authoritative sources for this effect.  Probably the GFCI manufacturers know all about it.

The bridge circuit which detects the flow imbalance depends on some precision electronics which are heat sensitive.  The heavy current itself does not affect them, but the side effect of that current heating up the components will lead to premature failure.