Trying to run

Trying to run a Managed Backup, but getting the following 502 error, once the backup reaches 44%, and took 4 hours:
https://static.livechatinc.com/8801096/P45JY246P4/7789d757259b7b4a4fea48db8657affb/Screen%20Shot%202018-02-22%20at%2002.14.56.png

Enabled Debug mode but it doesn't give any clue regarding the error.