Newest version: 6.4.2.6-4.1.3.0-54915 (was also running an older version with the same problem, so seems to not be version specific issue)
VOIP client is RingCentral Desktop
Band: Set to prefer 5Ghz, but operating on both 2.4Ghz and 5Ghz
Transmit power of the IAPs are min 9, max 24. I did have the max lower, but increased it to 24 for troubleshooting this issue which didn't seem to help. This morning I'm getting reports of people disconnecting when moving around the office instead of it roaming between the IAPs, not sure if related yet or not to this change.
Thanks!