Unable to execute group of unique appium tests in two sibling VMs running on a same host

Issues/Bugs
1

If a group of unique appium tests were executed only in either of sibling VM, then tests runs successfully.

If the same group of unique appium tests were exected in both the sibling VMs simultaneosuly, then tests fails with either of below errors:

Also, Appium server is running independently in each sibling VM.

Errors:

  1. org.selenium.WebdriverException: An unknown server-side error occurred while processing the command
  2. Connection refused error

PS:
VMs are installed with:

  • Appium and its prerquistes
  • intel HAXM
  • Android emulators/iOS simulators