What should you check first?
Look at several weeks rather than one bad workout. Review actual reps, load, RIR, missed sessions, sleep/recovery patterns, technique and whether other lifts are progressing.
Should you immediately add more volume?
Not necessarily. More work can solve insufficient stimulus, but it can worsen excessive fatigue. Change the variable that the evidence suggests is limiting progress.
Can changing a split help?
Sometimes. Redistributing work can improve recovery or increase useful exposure to a priority lift. A split change should solve a programming problem rather than provide novelty for its own sake.