Complex sentence: SNP support for a second referendum has been suggested to be a contributory factor to the party losing seats; the party secured 35 of the 59 Scottish seats in the 2017 United Kingdom general election, 21 fewer seats than in the 2015 election.
Split into simpler sentences: SNP support for a second referendum was suggested to be a contributory factor to the party losing seats in the 2017 United Kingdom general election. The party won 35 of the 59 Scottish seats, 21 fewer seats than in the 2015 election.