A couple things to note which aren't really related to your main question:
First, Ubuntu 16.04.x series is end of life. It's 5 year life cycle was from April 2016 to April 2021. For a VPN server you really should upgrade to 18.04 or 20.04.
Second, OpenVPN AS 2.8.7 is also out of date and the latest version of 2.8.8 addresses a critical security advisory issue.
More details about the AS 2.8.8 update is available here:
https://openvpn.net/vpn-server-resources/release-notes/
For the Log Reports issue, see if you can recreate the issue with the latest version of Google Chrome and Mozilla Firefox.
If you are still having problems, then try running the following commands:
sqlite3 /usr/local/openvpn_as/etc/db/log.db .databases
sqlite3 /usr/local/openvpn_as/etc/db/log.db .tables
If you get commands not found then you may need to run apt-get install sqlite3
If you get "Error: database disk image malformed" then that is the problem. I would then recommend contact OpenVPN AS support for how to fix the corrupted database file.
