SerialConnection port access not working on Ubuntu 18 but works on Ubuntu 13

I have a desktop app i developed a while back under Realbasic and ran on Ubuntu 13 32-bit version.
We now require to run our app under Ubuntu 18 so i am in the process of upgrading the code through the latest Xojo 2019r3.1.
My app commnucates with some propietry equipment via the serial oprt /dev/ttyS0
Under Ubuntu 18 i am able using a program called Serial Port terminal to sucessfully communicate with our equipment as expected, sending and receiving data.

When i try to run my software under Xojo the serial communication dones’t work, the DataReceived event never fires.

Just to be sure it wans’t my software, i followed the Xojo SerialController tutorial modifying it slightly so it communicates with our serial device but this didnt’ work.

I then tried running the same Xojo tutorial program on my old Ubuntu 13 PC and it worked straightaway on this. So the problem seems to lie with Ubuntu 18 and Xojo. Because the Serial Port Terminal program is able to access the serial port ok i don’t think it access rights stopping it.

One difference is also that Ubuntu 13 is 32-bit but Ubuntu 18 is now running my program in 64-bit, not sure if this is relevent to the problem.

Just wonder if anyone has had a similar issue or any suggestions to look at.