Does the log in the wp admin area look ok? Is it only the export log that are missing information? I just did a test on one of my current sites and the export seem to have all info there (like the name of the post that was updated, and similar).
Yes, the admin area looks okay. This is a snippet of what I see on my end with the export feature.
9/25/19 17:58 SimpleUserLogger info wp_user user_logged_in 1:58 pm (Sep 25, 2019 at 13:58) Logged in 1
9/25/19 17:56 SimplePostLogger info wp_user post_updated 1:56 pm (Sep 25, 2019 at 13:56) Updated "" 1
9/25/19 17:43 SimplePostLogger info wp_user post_updated 1:43 pm (Sep 25, 2019 at 13:43) Updated "" 2
9/25/19 17:38 SimplePostLogger info wp_user post_updated 1:38 pm (Sep 25, 2019 at 13:38) Updated "" 1
9/25/19 17:34 SimplePostLogger info wp_user post_updated 1:34 pm (Sep 25, 2019 at 13:34) Updated "" 1
Do you have any other plugins installed? Any change you can deactivate them and see if the problem is still there?