There are certain software versions of both fusion head units and Garmin plotters that are known to not play well together and cause locking up issues. Also some models of fusion head units can experience locking up issues sometimes from bad hardware straight from the factory (common on ra70, ra70n, ra70nsx), or bad original software in the case of early ra770's.
Most often it's related to issues with the nmea2000 network such as incorrect drop lengths, incorrect number of terminators, multiple power sources, unbalanced networks, etc.... all of which are fairly common unfortunately for ranger and cutwater boats straight from the factory.
Best way to troubleshoot is to isolate the stereo be unplugging the nmea2000 cable at the back of the unit and see if it suddenly works fine, and if so then start troubleshooting the whole network to find the issue (...fun...). Next would be to update the software of all the units via a USB connected to the back of the unit along with making sure the Garmin system is fully up to date as well via a card or active captain.