Craft in Docker throws '/app/web/cpresources doesn’t exist or isn’t writable by PHP'

Question

I'm trying to deploy a Dockerized Craft CMS website. The basic setup is as follows:

• craft running in Docker
• nginx running on the server, using proxy_pass to point to docker container

The setup itself seems to work, but Craft throws /app/web/cpresources doesn’t exist or isn’t writable by PHP when visiting the website (temporarily running dev mode on server to debug).

So far, to me this seems like a permissions issue. But I don't know how to properly solve it. Locally (MacBook Pro), this all works fine. It's on the server (Ubuntu 20.04) I suddenly encounter this issue.

docker-compose.yml

version: '3.6'

services:
  app:
    build:
      context: .
      dockerfile: ./.docker-config/php/Dockerfile
    container_name: app
    env_file: .env
    volumes:
      - ./.app-data/craft/web/cpresources:/app/web/cpresources
      - ./.app-data/craft/web/images:/app/web/images
    restart: unless-stopped

  nginx:
    build:
      context: .
      dockerfile: ./.docker-config/nginx/Dockerfile
    container_name: nginx
    ports:
      - 8000:80
    volumes:
      - ./.app-data/craft/web/cpresources:/app/web/cpresources
      - ./.app-data/craft/web/images:/app/web/images
    restart: unless-stopped

  database:
    image: postgres:12.4-alpine
    container_name: database
    env_file: .env
    volumes:
      - ./.app-data/database:/var/lib/postgresql/data
    restart: unless-stopped

  adminer:
    image: adminer:4.7.7-standalone
    container_name: adminer
    ports:
      - 8080:8080

Dockerfile (Craft)

FROM composer:2.0.4 as vendor
COPY ./craft/composer.json composer.json
COPY ./craft/composer.lock composer.lock
RUN composer install --ignore-platform-reqs --no-interaction --prefer-dist

FROM craftcms/php-fpm:7.4
COPY --chown=www-data:www-data --from=vendor /app/vendor/ /app/vendor/
COPY --chown=www-data:www-data ./craft/ .