FusionReactor has 2 ways of collecting data, one through a live tunnel to the instance and one through data packs.
If you see 'could not connect to FusionReactor agent' this would indicate there is an issue with the live tunnel connection.
This could be for a few reasons:
The live tunnel is only available when the instance is online, so certain actions will be unavailable if the instance is not running
Your instance is unable to connect to the live data tunnel (otherwise known as Cloud Connector)
There was an issue retrieving data from the live tunnel. This could be due to several reasons:
Data being returned is too large
The network connection to the server is too slow and is timing out
FusionReactor is running an old version where the data route is not available
If you are unsure contact us on the messenger and we can take a look.