I think custom Charts will only work with the following Garmin Plotters:
GPSMAP 400/500/600/700/1000/4000/5000/6000/7000 Series.
Garmin Plotters with a software version higher than 2015.02.02 will not be compatible.
As stated for example from this vendor about Navionics charts.
Code:
Please Login or Register to see the links
Changelog probably is this one:
Changes made from version xx to xx: Changes to support manufacturing.

The only way (if possible) is to downgrade fw.
Read info linked in post n 24.