The same thing happened to my Haus Pale ale. I took my thief and stuck it in then swirled up some yeast into suspension. It turns out my parents house went down to 60 degrees a couple of times overnight. That probably did it. A week later the beer went to the final FG with no other modifications required.
Yeah, we need mo' info. MO INFO! MO INFO! Recipe, fermentation temp, did you oxygenate/aerate it initially? I had a double IPA stall out around 1.040. Turns out it was actually just done.
for the sake of discussion, I just racked a Belgian Strong Dark Ale that had a OG of 1.103 and ended at 1.020, pitched on a yeast cake of WLP 500 and 570.