Only able to run a single device at a time in parallel in appium

I have tried: running parallel test scripts (using TestNg) by creating two instances of Appium server each with different port, UDID, and bootstrap. I setup the capabilities to match the corresponding instance and it does get executed but NOT parallel. Only one test will gets executed (sometimes in device A or sometimes in device B) in one appium instance and the second instance just halts. Sometimes device A will start running for a few seconds and once device B starts it will halt device A or vise versa.
Error Message :- “Cleaning up stale test sessions on the unregistered node”

@Rohit.Sh please check this hope it helps