helm-projectile-find-files does not use cached candidate list

for reference, my project is absolutely massive as it is a checkout of AOSP. find . | wc shows 1851855

Expected behavior

helm uses cached candidate list

Actual behavior

it appears that helm is always dropping into helm-get-candidates

Steps to reproduce the problem

sync AOSP: https://source.android.com/setup/build/downloading
add a known projectile project at the root
invoke helm-projectile-find-files

Backtraces if necessary (`M-x toggle-debug-on-error`)

profiler report:

- command-execute                                                4769  98%
 - call-interactively                                            4769  98%
  - funcall-interactively                                        4769  98%
   - helm-projectile-find-file                                   4769  98%
    - helm                                                       4761  98%
     - apply                                                     4761  98%
      - helm                                                     4761  98%
       - apply                                                   4761  98%
        - helm-internal                                          4761  98%
         - helm-read-pattern-maybe                               4757  98%
          - helm-update                                          4744  98%
           - helm--collect-matches                               4740  98%
            - helm-compute-matches                               4740  98%
             - helm-get-cached-candidates                        4728  97%
              - helm-get-candidates                              4728  97%
               - helm-interpret-value                            4728  97%
                - helm-apply-functions-from-source               4728  97%
                 - apply                                         4728  97%
                  - #<compiled 0x330b9d5>                        4636  96%
                   - projectile-current-project-...                  4   0%
                    - projectile-project-root                       4   0%
                     - apply                                        4   0%
                      - ad-Advice-projectile-pro...                  4   0%

Environment & version information

helm-projectile version: helm-projectile-20200625.443:

(define-package "helm-projectile" "20200625.443" "Helm integration for Projectile" '((helm "1.9.9") (projectile "2.2.0") (cl-lib "0.3")) :commit "2f3a2a03d6cb9419c25b432637aa11c8d2f9f3b7" :keywords '("project" "convenience") :authors '(("Bozhidar Batsov")) :maintainer '("Bozhidar Batsov") :url "https://github.com/bbatsov/helm-projectile")

helm version (in helm-pkg.el): helm-20200830.1534

(define-package "helm" "20200830.1534" "Helm is an Emacs incremental and narrowing framework" '((emacs "25.1") (async "1.9.4") (popup "0.5.3") (helm-core "3.6.2")) :commit "3ab96ee577006510ca18568dbb1b30956cf49225" :url "https://emacs-helm.github.io/helm/")

projectile version (M-x projectile-version): Projectile 20200822.822
Emacs version (M-x emacs-version): GNU Emacs 26.3 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.22.30) of 2019-09-16
OS: Ubuntu 18.04 LTS

bbatsov / helm-projectile