Hi there - has anything changed recently? someone's been to the vet, a new smell? new surroundings? anything?
Sometimes when there is a new smell around, my female Misty will chase her bonded mate Charlie because she thinks he's the wierd smell. I'm not sure why. If Charlie goes to he vet - he smells funny and she'll chase him around a bit.
When that happens, what I do is put some vanilla exract on a cotton ball and rub both of them on the top of theirs heads with it. Then they both smell the same and the chasing calms down.
If they are doing it on a regular basis, try a couple re-bonding tricks like taking them on a car ride together or putting them in a basket on top a washing machine that's on. It intriduces a bit of stress and causes them to turn to each other for comfort (and hopefully for get the chasing).
Nadia