acf short code not subsituted if used in nested page

I have a wordpress page which has contents like below Page 1

Flat [acf field="flat_number"]

[insert page='abbott-house-common-lock-box' display='content']

this page has advanced custom fields that define “flat_number” = 70 this page refers to anther page (slug abbott-house-common-lock-box)to be included as conent as you can se Page abbott-house-common-lock-box’ content below:

Walk straight downstairs and lot 60 is the first parking on your right side. The code for the GATE :?C7981X Find the lock box for your flat?[acf field="flat_number"]??using the picture above,? And then open the lock box to get the keys to enter the building using?combination code

Now, when I view page 1 outside the WP admin (in view mode), i see:

Line 1: Flat 70

but the line

“Find the lock box for your flat using the picture above, ” shows a big empty space around the place where I shoudl also have the flat_number being substituted

Why is this? is this because the acf short code is in a page included in a page?

Recently I migrated from from 5.6 to 6 , is that the reason?

The page I need help with: [log in to see the link]