Thanks for helping me work through this problem I believe I have resolved it now.
Apparently you have to enable the com port in Acemanager for the serial port to work. It is not enough to reserve the port for ALEOS and open the port in the LUA script it must be enabled. Or else you get odd behaviours like being able to send but not receive.
I’m not exactly sure if any of the settings in the comm port actually matter because in the lua script you specify baud rate etc. So my guess is it just needs to be enabled.
Again thanks for the help and Sierra Wireless directly for finding the problem.