nvs_set_str returns ESP_ERR_NO_MEM?

[freeride01]

Pretty much what the title says.
I'm trying to write a string to NVS flash with nvs_set_str. Sometimes it is successful, sometimes it returns ESP_ERR_NO_MEM, which is not even among the error codes it can return, according to documentation.
Checked heap and stack highwater mark, there is more than enough available.
Any idea what's going on?

[ESP_Sprite]

Just a guess, but possibly your NVS partition is full?