You need to run btrfs balance...here is everything explained: https://together.jolla.com/question/...ious-problems/
[nemo@Sailfish ~]$ devel-su Password: [root@Sailfish nemo]# btrfs-balancer allocation Total: 14763950080 bytes Used: 14098230149 bytes Allocated: 95 % [root@Sailfish nemo]# btrfs-balancer balance Balancing... 0 % Balancing... 10 % Balancing... 20 % Balancing... 35 % Balancing... 50 % Balancing... 75 % Balancing... 81 % Balancing... 89 % Balancing... 96 % Balancing... 96 % Balancing... 96 % Balancing... 97 % Balancing... 97 % Balancing... 98 % Balancing... 98 % Balancing... 99 % Balancing... 99 % Balancing... 100 % Finished. [root@Sailfish nemo]# btrfs-balancer allocation Total: 14763950080 bytes Used: 11950746501 bytes Allocated: 80 % [root@Sailfish nemo]#