ONe could say the same about campaigning when in office. Why don't we take a quick peak at missed votes.
From Jan 2007 to Jan 2020, Sanders missed 511 of 4,037 roll call votes, which is 12.7%. This is much worse than the median of 1.4% among the lifetime records of senators currently serving. The chart below reports missed votes over time.
Sen. Warren has missed 54.4% of votes in the 116th Congress (2019-20). This makes her the 4th most absent member of the Senate.