PHP-FPM docker container stops responding after a while (in some cases weeks) on Digital Ocean with Caddy

I have 3 different Ubuntu droplets with Docker on Digital Ocean. They are all running Caddy as proxy with 2 of them using PHP-FPM and 1 using PHP-FPM Alpine.

After the server has been running a while, sometimes a few days, sometimes 3-4 weeks, the request stops responding.

All has the same type of problem.

I can SSH into the droplet. The caddy seems to be running all fine. I can access everything through caddy that is not the PHP.

The interessting part from the Caddy Docker log is this:

{
  "level": "error",
  "logger": "http.log.error",
  "msg": "dialing backend: dial tcp 172.30.0.3:9000: i/o timeout",
  "duration": 3.014910236,
  "status": 502,
  "err_id": "j14574vxr",
  "err_trace": "reverseproxy.statusError (reverseproxy.go:1196)"
}

If I do a docker logs -f PHP_CONTAINER all I can see is a valid request from the time before PHP stopped responding.

If i restart only the PHP container it starts working again. The strange part is that if I ONLY do a restart of CADDY container it will also start working.

I didn't seem to have this problem with NGINX earlier. So I my initial thought was that CADDY was the problem. But I do get connection to other services on the same Docker server. For instance PHP-FPM service doesn't respond, but my phpMyAdmin service is still working.

The caddy file is like this:

mydomain.com {
    root * /var/www/public
    php_fastcgi /* php:9000
    file_server
}

The PHP-FPM Dockerfile is like this:

FROM php:8.1.6-fpm

ARG user
ARG uid

RUN apt-get update && apt-get install -y \
    curl \
    zip \
    unzip

RUN apt-get clean && rm -rf /var/lib/apt/lists/*

COPY --from=composer:latest /usr/bin/composer /usr/bin/composer
r
RUN useradd -G www-data,root -u $uid -d /home/$user $user
RUN mkdir -p /home/$user/.composer && \
    chown -R $user:$user /home/$user

WORKDIR /var/www

USER $user

I have tried multiple versions of PHP-FPM, it still happening.

For my WordPress site, using the FPM-Alpine version, I basically use the same Dockerfile as this (some smaller modifications only) https://github.com/docker-library/wordpress/blob/master/latest/php8.1/fpm-alpine/Dockerfile

Does anyone has tips to what I can try to figure out why this error keeps happening.