I am also facing this issue sometimes.
and the output of influxd config | grep -i index is
Merging with configuration at: /etc/influxdb/influxdb.conf
index-version = “inmem”
Starting with the InfluxDB 1.6 release, enabling Time Series Index (TSI) is recommended for all customers. To learn more about TSI, see:
* [Time Series Index (TSI) overview](https://docs.influxdata.com/influxdb/v1.7/concepts/time-series-index/)
* [Time Series Index (TSI) details](https://docs.influxdata.com/influxdb/v1.7/concepts/tsi-details/)
The upgrade steps below guide you in upgrading InfluxDB OSS and InfluxDB Enterprise, enabling TSI functionality.
> ***Note:*** For the InfluxDB 1.7 release, the default continues to use TSM-based shards as in earlier versions, with in-memory indexes.