Yes, this is on the mailbox features tab as you suggest. The Adaxes version is 3.11.16825.0. I enabled tracing and there are no error messages in the trace, the only thing I see is the following. Before I turned on tracing, I was able to get it to work one time with a particular user, but I can't get it to work at all now after trying with a dozen or so users.
[09/11/2019 10:07:53] Get-Mailbox -Identity "Redacted"
[09/11/2019 10:07:54] Succeed
[09/11/2019 10:07:54] Get-UMMailbox -Identity "Redacted"
[09/11/2019 10:07:54] Succeed
[09/11/2019 10:07:54] Get-UMMailboxPIN -Identity "Redacted"
[09/11/2019 10:07:55] Succeed
[09/11/2019 10:07:55] Get-CASMailbox -Identity "Redacted"
[09/11/2019 10:07:55] Succeed
[09/11/2019 10:07:57] Get-MobileDeviceStatistics -Mailbox "Redacted"
[09/11/2019 10:07:58] Succeed
[09/11/2019 10:09:13] Get-Mailbox -Identity "Redacted"
[09/11/2019 10:09:13] Succeed
[09/11/2019 10:09:13] Get-UMMailbox -Identity "Redacted"
[09/11/2019 10:09:13] Succeed
[09/11/2019 10:09:13] Get-UMMailboxPIN -Identity "Redacted"
[09/11/2019 10:09:15] Succeed
[09/11/2019 10:09:15] Get-CASMailbox -Identity "Redacted"
[09/11/2019 10:09:15] Succeed
[09/11/2019 10:09:24] Get-MobileDeviceStatistics -Mailbox "Redacted"
[09/11/2019 10:09:25] Succeed