Hi,
First, I would note that you appear to be running an out-of-date version of InfluxDB 1.8 - something like from 2022
From the website https://www.influxdata.com/downloads/
I see the current download for RHEL for AMD64 servers, is done with this command for version 1.11
wget https://download.influxdata.com/influxdb/releases/influxdb-1.11.8.x86_64.rpm
sudo yum localinstall influxdb-1.11.8.x86_64.rpm
I would upgrade in case you have hit an already fixed bug.
You have already verified that there is sufficient disk capacity - full marks.
I would also check for errors reported by the OS (RHEL) and NAS, in case your NAS has failed.
Then I would check the InfluxDB and Grafana log file in case they are reporting errors.
Next, I would create a very simple NEW Grafana and check whether you can see the missing data period or not.
This might eliminate any problems in data access.
Finally, you could go see the underlying data inside InfluxDB. This is not easy and is made harder due to the size of your database, as a simple SQL-like command, your output may be millions of rows of data.
Very briefly, a starter for ten:
Start the test access with the influx command (from memory, you need to find the V1 documentation for the CLI)). Assuming you have a virtual machine called "fred".
influx
> show databases
> use njmon
> show measurements
> show tag keys
> show field keys
> select last(*) from timestamp where ("host"="fred" )
> select count(*) from timestamp
Note: timestamp is a measurement name (a small measurement). Might take a long time as it counts for all time and all servers!
> select count(*) from timestamp where time > '2025-06-01'
Guess here - I am not online to check:
> select count(*) from timestamp where ( time > '2025-06-01' and "host" = "fred")
You have backups of the InfluxDB, right?
Best of luck, N