Downgrading back to 9.6 (if you are not using 9.7-specific features) would tell us a lot. If the problem persists then we know it is probably un-related to the code, and likely something environment related.
Upgrading reset the stored ChannelFly data and so the AP had to re-learn the environment. It should still settle down on it's own eventually unless you have a lot of dynamic interference.
On a standalone AP, static channels are currently the only workaround. You could let ChannelFly run for a while, then lock it in (see below)
If you grab the AP supportinfo file you can look for "channelfly" and that will tell you the current status of the system and the stats on each channel. At the bottom of that, search for num_chan and that will tell you how many times it's switched.