Your comments

I believe NMEA0183 is built on RS232 or serial port hardware.

This hardware is not supported with IQAN products without some sort of gateway to convert it to CAN.

if you are replacing an XA2 in an existing system, the ID tag should already be in the harness.

Can you confirm that the display brightness was not inadvertently turned down to 0%, making it appear to not function?

Please see product link below:

The Instruction Book (Appendices) or CAD documentation should provide what you need.

You do not need to use an IQAN display.  You can accomplish what you need with an IQAN MC41, assuming the analog throttle signal meets the capabilities of the MC41.

MC3 is in phase out.  You should investigate, but costwise it might be better to use 4 x MC41 than 2 x MC3.

If it's occurring on start up, the likely causes are battery voltage exists on an output before the module powers up or a slow rise in power supply voltage.  Possible causes are covered in appendix B of the instruction book.

Try using a static local variable in your Qcode to retain the latched state.  You can use if/then to manipulate the state.  Result will always be your static variable.

This can be done already, although you have to define your frame channels as GFIN / GFOUT for J1939 messages.  This should be a work around for now.

Are you using the battery charger as a power supply for the system?  

I have seen cases where this has been attempted and as soon as the system draws any significant load, the charger output will drop out.  Going above 14V generally may cause the system to draw more current, hence, dropping supply of the module below the accpetable operating threshold.  If you are using a battery charger, please try while a good battery is connected as well.  Or use a benchtop power supply.