Aside from vaporware status the first two years, the 2.0 UPGRADES list spells out the issues; the biggest one was tablet charging and related battery issues.
Others listed are software glitches, questionable gain curves and mapping functionality. Maybe it was lacking a simulation mode as well?
Copy and paste of listed upgrades:
LONGER BATTERY LIFE
The new RT-9 2.0 comes with our new LifePO4 10aH lithium battery with a 3aH rapid charger, allowing for over 10 hours of continuous use, so you’ll be set for the entire day on the ice. The LiFePO4 is also considerably lighter than the traditional SLA batteries, making it more efficient to use on the go.
UPGRADED CIRCUITRY & SOFTWARE
The RT-9 2.0 has upgraded circuitry and software to give a much more user-friendly experience. There is no longer any low battery issues, screen glitching or software bugs. The sonar experience is better than ever. A few of the improvements include:
ABILITY TO ENTER YOUR OWN WAYPOINTS
Whether you want to enter your summer waypoints or have waypoints from a friend, you can now manually enter them into the RT-9 2.0.
IMPROVED GAIN CURVES
We have improved the gain curves, fine-tuning your ability to find and identify more fish.
IMPROVED EXTERNAL BATTERY CUT-OFF
You now get a longer run time off of the current system, complementing the new LiFePO4 battery addition, giving you the best experience possible with the RT-9 2.0.
ICE AND OPEN WATER SIMULATOR
You can now familiarize yourself with the RT-9 by using the new simulator mode, before hitting the ice or open water.
NAVIONICS + USA AND CANADA CHIP NOW INCLUDED
The MarCum RT-9 2.0 now comes standard with Navionics+ USA and Canada Chip. The mapping chip retails for $199 MSRP when purchased by itself, allows anglers to have detailed mapping of any location in the USA and Canada. The chip is now included in the RT-9 2.0