It is difficult to say where the problem is but your new combination should work. I am using the Craft&Theory cable shown in the FrSky Telemetry page of the APM Wiki. I have used this cable on several projects between a Pixhawk v2.4.8 clone and an X8R receiver. On another project, I also used a Pixracer directly connected to an X8R receiver which was pretty cool.
Make sure that your SERIAL#_PROTOCOL parameter is set to 10 for passthrough SmartPort telemetry. Also, be sure that you have enabled LUA scripts on your Radio Type screen in OpenTX Companion and that you discovered your sensors after the upgrade to v2.1.9.