Return code 137 when building docker image

Since today I get return codes 137 at varying stages of the process when I try to (re-) build my docker image chockemeyer:rservers.
I found some posts on this topics on the web - they all refer to memory problems. However, top shows me some 12-13 GB memory are free.
Most times, it stops somewhere during the Rscript command.
The dockerfile:

FROM ubuntu:18.04
# I chose ubuntu as basis as it is my actual system

MAINTAINER Cord Hockemeyer <>

WORKDIR /install
ADD . /install

ENV TZ=Europe/Vienna
RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone

# Installing some needed ubuntu packages including R
RUN apt update && apt install -y apt && apt dist-upgrade -y && apt install -y software-properties-common libgslcblas0 libgsl-dev mesa-common-dev libglu1-mesa-dev gnupg jags vim
RUN apt install -y gdebi-core curl openssl libssl-dev libcurl4-openssl-dev libcairo2 ed libcairo2-dev libxml2-dev libxt-dev libv8-dev

RUN echo "deb bionic-cran35/" >>/etc/apt/sources.list
RUN apt-key adv --keyserver --recv-key E084DAB9
RUN apt update && apt install -y r-base r-base-core r-base-dev r-base-html r-doc-html r-recommended

# The following command assumes that only the current RStudio Server and
# Shiny Server installation packages are located in this directory!
RUN gdebi -n shiny*.deb && gdebi -n rstudio*.deb

RUN Rscript R-packages.list # R scipt installing all the R packages needed including shiny and rmarkdown

EXPOSE 3838 8787

CMD ["/install/start-servers"]

Any help would be strongly appreciated!

Thanks, Cord