buildkit: Layer in built image is missing / empty 0B

Since upgradeing to v0.8.1 from v0.8.0, I encounter a missing layer, or at least a missing file in the built image. When trying to start the image, it fails, because the entrypoint file is missing. I can confirm this, if I override the entrypoint and start the image, the docker-entrypoint.sh isn’t there. I could reproduce this for multiple builds in CI, after downgrading, the bug was gone.

My Dockerfile has this structure:

# Install php dependencies
FROM composer:1 AS php-dependencies

COPY composer.lock composer.json ./
RUN composer install --ignore-platform-reqs


FROM php:7.4-cli AS base

WORKDIR /application

# ... some stuff

# Configure entrypoint script
COPY dockerfiles/php/docker-entrypoint.cron.sh /docker-entrypoint.sh
RUN chmod +x /docker-entrypoint.sh
ENTRYPOINT ["/docker-entrypoint.sh"]


FROM base AS production

# Copy built dependencies and src
COPY --chown=33:33 . .
COPY --from=php-dependencies --chown=33:33 /app/vendor ./vendor