I dont have a F2, I have the F4 but I have seen this happen also. I would think the F2 and F4 will act similarly, but this might not be the case. Usually I just turn down the sensitivity in that area.
It could also mean you are in a trashy area with multiple targets. One thing I do if I think there are several in one area is to lift the coil off the ground a few inches to try and separate the targets or I just toss the 4" coil on.
The F4 is also susceptible to electronic interference, it is possible you were near power lines (over or under) or a cell tower etc. Mine also starts to act up when the battery gets low.
The F4 will also jump around if the target is trash, but usually not all that much.
GL and HH