516 /dev/md127 suddenly read only- although space available

All my shares became suddenly read only although there is still 4TB free . After a reboot it was writeable for an hour but now it is again RO. OS version is latest 6.2.3 balance is done weekly.

What can I do?

root@nas1:/data/daten# btrfs filesystem show
Label: '7c6e49a2:root' uuid: 72ce1783-d430-4507-b346-48dae62b47f9
Total devices 1 FS bytes used 1.09GiB
devid 1 size 4.00GiB used 4.00GiB path /dev/md0

Label: '7c6e49a2:data' uuid: 4f716840-2b0d-4723-bbda-2d0ef4cc249e
Total devices 1 FS bytes used 13.28TiB
devid 1 size 18.17TiB used 13.81TiB path /dev/md127

root@nas1:~# btrfs filesystem df -h /data
Data, single: total=13.78TiB, used=13.27TiB
System, DUP: total=32.00MiB, used=1.91MiB
System, single: total=4.00MiB, used=0.00B
Metadata, DUP: total=17.00GiB, used=15.81GiB
root@nas1:~#

Mount
/dev/md127 on /data type btrfs (ro,noatime,nodiratime,nospace_cache)
/dev/md127 on /home type btrfs (ro,noatime,nodiratime,nospace_cache)
/dev/md127 on /apps type btrfs (ro,noatime,nodiratime,nospace_cache)
/dev/md127 on /var/ftp/home type btrfs (ro,noatime,nodiratime,nospace_cache)
/dev/md127 on /var/ftp/ccu type btrfs (ro,noatime,nodiratime,nospace_cache)
/dev/md127 on /var/ftp/media type btrfs (ro,noatime,nodiratime,nospace_cache)
/dev/md127 on /run/nfs4/data/ccu type btrfs (ro,noatime,nodiratime,nospace_cache)
/dev/md127 on /run/nfs4/data/ccu-historian type btrfs (ro,noatime,nodiratime,nospace_cache)
/dev/md127 on /run/nfs4/data/filme type btrfs (ro,noatime,nodiratime,nospace_cache)
/dev/md127 on /run/nfs4/data/media type btrfs (ro,noatime,nodiratime,nospace_cache)
/dev/md127 on /run/nfs4/data/sabnzbd type btrfs (ro,noatime,nodiratime,nospace_cache)
/dev/md127 on /run/nfs4/home type btrfs (ro,noatime,nodiratime,nospace_cache)
tmpfs on /data/daten/snapshot type tmpfs (rw,noatime,nodiratime,size=4k)