The issue (CSCwd63665) have been seen on c9800-CL @ 17.6.4 with 49 APs (9120axi / 9124axi) and FlexConnect, too.
Some - not all - APs seemed to not answer the association request of clients.
Rebooting the APs helped for a short period of time.
Other customers running same version and AP-Types in local mode didn't report those issues.
After upgrading the FlexConnect installation to 17.9.4a the issue seems to be gone.
Tests are running for verification.
