Check the elastic config for data dir settings, and the ES API too on all servers.
I find this at your logs.
Xfs mark 5% of disk, and you have only 5% disk left
you also can check lsof, what files used by ES, and/or find to find the modified files from the last few hours.
using  data paths, mounts [[/ (rootfs)]], net usable_space [887.5mb], net total_space [49.9gb], spins? [unknown], types [rootfs]
Maybe the elastic cant write another (not data) file.
Second, (not related)
As far as I know, the ES recommendation for shard size is 20-40GB/shard. I suggest decrease the shards number for small indices and/or change retention policy (eg. 20GB max, 30 pcs -> 40GB, 15 pcs)
You have 6 servers, are you sure you don’t need to use replicas?