It appears that AirWave 8.2.9.0 can't process AMON User data from AOS 8.5.0.0.
When prefering AMON in AirWave you won't get any client count.
Workaround is to go into AMP Settings and change Additional AMP Services, Prefer AMON vs SNMP Polling set to No.
tailf async_logger_client
Wed Jul 3 13:56:22 2019: try_ap: id: 5
Wed Jul 3 13:56:22 2019: Use of uninitialized value in string eq at /usr/local/airwave/lib/perl/Mercury/AP/Aruba/Parser/AMONClientBase.pm line 128.
Wed Jul 3 13:56:22 2019: try_ap: id: 5
Wed Jul 3 13:56:22 2019: Use of uninitialized value $_ in hash element at /usr/local/airwave/lib/perl/Mercury/AP/Aruba/Parser/AMONClientBase.pm line 71.
Wed Jul 3 13:56:22 2019: try_ap: id: 5
Wed Jul 3 13:56:22 2019: Use of uninitialized value $_ in hash element at /usr/local/airwave/lib/perl/Mercury/AP/Aruba/Parser/AMONClientBase.pm line 72.
Wed Jul 3 13:56:22 2019: try failed! ap_id: 5 Can't use an undefined value as a HASH reference at /usr/local/airwave/lib/perl/Mercury/AP/Aruba/Parser/AMONClientMixin.pm line 88.
Aruba TAC ticket already opened, hopefully th defect will get resolved soon.