This article will discuss a possible scenario when configuring an interface with an L3 subinterface using the Mist dashboard will lead to a commit error

• An L2 interface being converted to an L3 subinterface
• Configuring GE and XE to coexist on the same interface
• The following commit error will appear on switch insights 

The underlying issue is that the "flexible-vlan-tagging" knob added during the L3 subinterface configuration attempts to use the VLAN ID from the previously existing Unit 0, causing it to fail and generate the commit error we saw.

This commit error can be verified by manually adding the configuration via the CLI and running a "commit check" (Note that you must roll back the changes to avoid inconsistencies.)

To avoid this, the port must adopt a profile that generates a change to unit 0; similarly, when the L3 subinterface unit is generated, it must completely replace Unit 0

Likewise, there may be cases where the interface configuration is duplicated in ge, xe, and et; therefore, the profiles among these can affect the configuration change and cause confusion. It is advisable to review and, if necessary, remove the configuration specifically in the ports section: