Sure. Using Cody Bellinger as an example:
All Games: 128 G, 901.1 P, 7.04 P/G
v. R 118 G, 632.2 P, 5.36 P/G
v. L 86 G, 268.9 P, 3.13 P/G
The split games are counting every game Bellinger faced either a lefty or a righty. So, it double counts the games when he faces both types of pitchers. Thus, it effectively has the wrong denominator when calculating the P/G.