This article provides solution to an issue where Flexible-vlan-tagging option is not available under interface-range hierarchy after upgrading device to version 23.4R1 or higher.

On SRX3xx series configured with flexible-vlan-tagging, after upgrading the device to Junos version 23.4R1 or higher the flexible-vlan-tagging option is missing under the interface hierarchy. This leads to a syntax error, stopping users from setting the flexible-vlan-tagging.

This is a known issue and has been addressed in the following releases - 23.4R2-S5, 24.2R2-S1, 24.4R1-S3, 24.4R2, 25.2R1

Please refer to the following link for more information - PR1853238