Same issue here. gone crazy trying to solve.
Edit: i think my problem is low storage. just check your storage first. when it's low, kibana auto changes its config to read-only mode. to deal with it, go to your dev tools console and
run below command:
PUT .kibana/_settings
{
"index": {
"blocks": {
"read_only_allow_delete": "false"
}
}
}