The snopes link is correct that extrapolating from the Old Dominion study is folly, but misses the point of the study:

"We find that non-citizen participation in U.S. elections is low, but non-zero...and (has) the potential to change important election outcomes."
https://ww2.odu.edu/~jrichman/NonCitizenVote.pdf

So the point is neither that zero non-citizens voted as snopes seems to assert or 5.7 million voted as others assert, but that enough might be voting to change the outcomes of close elections, so we should further examine that possibility. Which is what the commission is doing.

More:

"With these latest additions, the database now documents 581 cases of proven voter fraud and 848 criminal convictions."
http://dailysignal.com/2017/06/30/growing-pile-data-shows-voter-fraud-real-vast-problem/

"Approximately 2.75 million people have registrations in more than one state."
http://www.pewtrusts.org/~/media/legacy/uploadedfiles/pcs_assets/2012/pewupgradingvoterregistrationpdf.pdf