With a default Manjaro installation it may create hair-pulling issues as boot is on btrfs and btrfs uses compression which may cause non booting systems.
A very informative topic on btrfs Btrfs Best Practice
The Manjaro wiki page Btrfs - Manjaro
This is one of the reasons I wrote this guide 
- btrfs filesystem does indeed need special attention - both with troubleshooting and with maintenance Basic Manjaro rescue and Recovery