OK, self healed it... But for anyone else searching this error, refer to this thread:
In short, due to some space issue, it appears the indices were put into read only mode. My Kibana index was set as such so this console command fixed it:
PUT your_index_name/_settings
{
"index": {
"blocks": {
"read_only_allow_delete": "false"
}
}
}
Other indices may also be in that state so I'll check.