Docker Container - source files disappearing

A docker image I am creating and sending to a client is somehow deleting its source code 24-48 hours after it is started. We can see this by exec onto the running container and talking a look around.

The service is a simple flask app. The service doesn't go down as the application doesn't experience an issue but the static files it should be yielding go missing (along with everything else copied in) so we start getting 404s. I can't think of anything that would explain this (especially considering that it takes time for it to occur)

FROM python:3.8-slim-buster

ARG USERNAME=calibrator
ARG USER_UID=1000
ARG USER_GID=$USER_UID

RUN apt-get update \
    && groupadd --gid $USER_GID $USERNAME \
    && useradd -s /bin/bash --uid $USER_UID --gid $USER_GID -m $USERNAME \
    && apt-get install -y sudo \
    && echo $USERNAME ALL=\(root\) NOPASSWD:ALL > /etc/sudoers.d/$USERNAME\
    && chmod 0440 /etc/sudoers.d/$USERNAME \
    # Install open-cv packaged
    && apt-get install -y libsm6 libxext6 libxrender-dev libgtk2.0-dev libgl1-mesa-glx \
    #
    ## Git
    && sudo apt-get install -y git-lfs \
    #
    ## Bespoke setup
    && apt-get -y install unixodbc-dev \
    #
    ## PostgresSQL
    && apt-get -y install libpq-dev


ENV PATH="/home/${USERNAME}/.local/bin:${PATH}"

ARG git_user
ARG git_password
RUN pip install --upgrade pip
RUN python3 -m pip install --user git+https://${git_user}:${git_password}@bitbucket.org/****  


WORKDIR /home/calibrator

COPY requirements.txt requirements.txt
RUN pip install --no-cache-dir -r requirements.txt

COPY app app

ENV FLASK_APP=app/app.py
EXPOSE 80
STOPSIGNAL SIGTERM
CMD ["uwsgi", "--http", ":80", "--module", "app.app", "--callable", "app", "--processes=1", "--master"]

version: "3.7"
services:

  calibrator:
    container_name: sed-calibrator-ui
    image: sed-metadata-calibrator:2.0.3
    restart: always
    ports:
      - "8081:80"
    environment:
      - STORE_ID=N0001
      - DYNAMO_TABLE=****
      - DYNAMO_REGION=****
      - AWS_DEFAULT_REGION=****
      - AWS_ACCESS_KEY_ID=****
      - AWS_SECRET_ACCESS_KEY=****

The application reads in a single configuration file and connects to a database on startup and then defines the endpoints - none of which touch the filesystem again. How can the source code be deleting itself!?

Creating a new container resolves the issue.

Any suggestions in checking the client's environment would be appreciated because I cannot replicate it.

Clients versions

• Docker Version - 18.09.7
• Docker Compose version - 1.24.0

from Docker Container - source files disappearing