Hello i have the same problem restoring a backup file here is the log
Date: 2019-03-04 10:33:00
Backup Method: reload
Restore Method: external
User Mode: free
BackupGuard version: 1.1.82
Supported archive version: 5
Database prefix: wphn_
Site URL: https://www.j-emm.it
Home URL: https://www.j-emm.it
Uploads path: /home/ukgravel/public_html/j-emm.it/wp-content/uploads
Site installation: standard
OS: Linux
Server: Apache
User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36
PHP version: 5.6.40
SAPI: cgi-fcgi
MySQL version: 5.6.40
Int size: 8
Int lib: bcmath
Memory limit: 768M
Max execution time: 120
Disk free space: 933GB
Archive Size: 203.4MB (203445528 bytes)
Environment: WordPress 5.1
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Archive version: 5
Archive database prefix: wp_
Archive site URL: https://www.j-emm.it
2019-03-04 10:33:00: SGException: Seems you have changed database prefix. You should keep it constant to be able to restore this backup. Setup your WordPress installation with wp_ datbase prefix. [File: /home/ukgravel/public_html/j-emm.it/wp-content/plugins/backup/com/lib/SGArchive.php, Line: 483, URL: /bg_restore.php?k=4f2f8b2d5a7ddc890ba7123a21a1bdcc&action=awake]