Metronome does not stay constant in some bars (file imported from a pdf)

Hi, I find when importing pdfs that during playback sometimes the metronome does something rather strange - either starts clicking lots of beats or goes slower for one bar - anyway it seems to go out of time. Is there a way to modify this rather than deleting the whole bar, inserting a new bar and manually writing the notes in? Play bar 10 in the example below. Seems to do it in all my pdf imports.