Thanks for your time and reply.
I'm connecting only one microcontroller at a time. Before this EFM8UB3 device I tried with EFM8UB2. But EFM8UB2 did not get detected as HID due to issue in factory bootloader. That they conformed through errata notification. That issue resolved in EFM8UB3 and it gets detected as HID when I connect it to my USB port. Still don't know why it's not programming.
Please let me know if you need any more information for better understanding of this scenario. Once again thanks for your time.