back-end page builder is broken

Question

I took over a wordpress website, built with ACF and wp-bakery. If i create a new page, the wp-bakery builder works fine, however, the older pages only show some code. Here is a small example of code that the back-end builder shows:

<!-- wp:acf/flexible-columns {
"id": "block_60132831da1bd",
"name": "acf\/flexible-columns",
"data": {
    "column_0_flexible_columns_block_0_header_home__tagline": "",
    "_column_0_flexible_columns_block_0_header_home__tagline": "field_60128b601d299",
    "column_0_flexible_columns_block_0_header_home__title": "Groot ledscherm huren",
    "_column_0_flexible_columns_block_0_header_home__title": "field_60128b8e1d29a",
    "column_0_flexible_columns_block_0_header_home__text": "Kies uit ons ruime verhuuraanbod en huur een ledscherm met hoge beeldkwaliteit voor jouw bedrijf of vereniging. Ledscherm op aanhangwagen of op mobiele totem, aan jou de keuze.​",
    "_column_0_flexible_columns_block_0_header_home__text": "field_5efc4a062d911",
    "column_0_flexible_columns_block_0_header_home__cta_1": {
        "title": "Contacteer ons",
        "url": "\/nl\/contact\/",
        "target": ""
    },
    "_column_0_flexible_columns_block_0_header_home__cta_1": "field_60128bb51d29b",
    "column_0_flexible_columns_block_0_header_home__cta_2": {
        "title": "Onze producten",
        "url": "\/nl\/producten\/",
        "target": ""
    },

I have tried ACF flexible columns plugin, but that does nothing. I have also tried some other plugins that have either flexible, columns or ACF in the name. But I haven't found what the problem is. The front-end of the website works fine. I just can't edit older pages.