Hi 
!
For a way to set scan_interval for modern HA integrations (you don’t anymore) see Fronius power meter (and inverter) - help with configuration - #35 by farmio
That said, 10 seconds is the minimum HA allows as far as I’m concerned.
What data would you need this frequently? The new integration has different update intervals for its endpoints and slows down after some unsuccessfull requests (see documentation.
There was a minor bugfix in 2021.12.4 did you use this, or a later version?
There is no standing connection between HA and your inverter. HA requests data, Datalogger answers, end of communication until the next request (previously scan interval). Solar.web (and the Fronius App which uses that as well) will show you cached data on their servers - if your device doesn’t have a connection for a few minutes (or even hours) it will not be visible in Solar.web.
Symo and Hybrid should just behave exactly the same. That said we don’t have any test data for Hybrid inverters. Maybe you can generate some?
Its really not obvious what’s “out” 
The old integration uses the very same library to retrieve data from the inverters (pyfronius). You can always use a custom component - it would precedence over the core integrations.
Since you are the first one reporting such problems its very likely that the source of your problems lies in your specific setup.
- Are your inverters connected via their internal Wifi?
- Are there any log entries regarding the
froniusintegration? - What are the exact symptoms when you experience a “lost connection” (eg. entities states “unavailable”)
- How did you configure the old integration (yaml)?
- What exact firmware version do your Dataloggers run (you can see this in HA within the
SolarNetdevices page)?