I’d first look into this problem. If every 4 hours your node changes its status from Enabled to something else, then there is a problem with your setup other than debug.log which can live without being cleared for some days, no doubt. What status your node is showing? Do you check your status here: https://smartcash.bitcoiner.me/smartnodes/list/
What VPS provider are you using? Are there usage statistics of Memory/CPU? Do they look ok? If they look fine, I’d be first thinking of reinstalling the node from scratch, maybe you’ve corrupted files during installation.
P.S.The line crontab -e normally gives you “No such file, using a new one”, because you are creating it. When you call crontab -e next time, it should then just open it without a warning.