If: env(STAGE_BUILD) = true does not work in conditional stage

I have a .travis.yml defined like this , and I have env vars defined in settings

language: go
go: 1.14.x

services:
  - docker

branches:
  only:
#    - master
    - develop
    - /^release-[0-9]+\..*$/

stages:
#  - unit-test # Not implemented yet
  - build
  - build ppc
#  - test-e2e # Not implemented yet
#  - Git Clone 2.3
  - FVT 2.3

  - Git Clone my
  - FVT Deploy my
  - FVT Test Install
  - FVT Test Functions
  - FVT Test Uninstall

  - manifest
jobs:
  include:
    # Build and push image for all architectures
    - stage: build
      if: env(STAGE_BUILD) = true
      env: ARCH=linux
      os: linux
      script:
        - make docker/registry/login
        - make unittest
        - make build

    - stage: FVT 2.3
      if: branch = release-2.3
      script:
        - make fvt

    - stage: Git Clone my
      if: branch NOT IN (my-feature, release-2.3)
      env: 
      script:
        - make fvt-git-clone-my
    - stage: FVT Deploy my
      if: env(STAGE_DEPLOY) = true AND branch NOT IN (my-feature, release-2.3)
      script:
        - make fvt-deploy-my
      
    - stage: FVT Test Install
      if: env(STAGE_FUNCTION) = true AND branch NOT IN (my-feature, release-2.3)
      env: CMD=installTest
      script:
        - make installTest
    - stage: FVT Test Functions
      if: env(STAGE_FUNCTION) = true AND branch NOT IN (my-feature, release-2.3)
      env: CMD=functionTest
      script:
        - make functionTest
    - stage: FVT Test Uninstall
      if: env(STAGE_FUNCTION) = true AND branch NOT IN (my-feature, release-2.3)
      env: CMD=uninstallTest
      script:
        - make uninstallTest
        
$ export STAGE_FUNCTION=true
$ export STAGE_DEPLOY=true
$ export STAGE_BUILD=true

But the build stage is always ignored by Travis. And other stages are all executed.

Can I see the project in question? Another thing I would note is, since the script hook is not defined on the top level in this .travis.yml, the default is used in the jobs that do not have it explicitly defined.

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