Manager's lastline test appliance output reports 'Login Failed'.
On-Prem , in 9.8 release , this issue would be seen
This is due to a known issue with pcapapi. It errors out whenever it has to deal with the analysis of a pcap contains DNS traffic.
This is observed in monitoring logs too.
The third screenshot shows the expanded error for Type 'pcapapi.analysis'.
The problem is fixed in 9.8.1