Is this a stationary or mobile client? If mobile, looks normal to me. the timestamps have decent gaps in between them.
If stationary, then the client is moving because signal is weaker and it hits whatever internal mechanism threshold that tells it to look for a stronger signal.
Are your access points statically configured channel/power? If not, then maybe they are changing power or channels, causing the client to 'find' another AP when it happens. I would recommend checking those settings to see how they are configured.
If you go to the AP, RF tab, you can see 'events' up at the top, and you might be able to correlate those with the times the client roamed etc.