I can see the following message in your Apache error log:
The timeout specified has expired: [client <redacted>] AH01075: Error dispatching request to : (reading input brigade), referer: http://<redacted>/wp-admin/admin.php?page=ai1wm_import
This error can also found in cases where an increasingly common issue is happening. Could you check if applying this change in the Apache configuration solves this issue for you as well?
As mentioned in that thread, there is an open ticket in our bug-tracking system and we are currently looking into it.