Why was I banned?

Because I used Stockfish against the lichess Stockfish? [ALLOWED]
Or because of the studies I created "Stockfish vs. Real People" in which I imported games from different sites?

This may not answer your question, but I could not find much evidence after 1 minute of searching... anyway, if you want your ban removed, the only way is to contact lichess.

en.lichess.org/contact