In his look at the Reds at mid-season, Kyle Nagel notices what should be a positive isn’t reflected in the runs column:

The Reds are second in the NL in runners left on base (673), just four behind Los Angeles.
Opponents, though, are still finding ways to score. The Reds, due in part to a suspect bullpen, rank 12th in the NL in ERA, at 4.78.

Often, lots of men on base mean lots of men left on base. And lots of men on base usually means lots of men scoring. However, the Reds are seventh in the NL in OBA allowed, certainly not terrible. They’ve given up a very high slugging percentage, but that should tend to clear the bases. On top of that, opponents are hitting very well with runners in scoring position. However, with two out and runners in scoring position, Reds pitchers tend to walk batters or get an out. I can see where that would lead to lots left on base.