Dockerfile build inconsistency in a Jenkinsfile (Connection failed error) - docker

Question

In my Jenkins CICD pipeline, I have stage where I build my backend image.
stage('Build Backend Image') {
steps {
sh '''
docker login -u <id> -p <pw> <dockerhub>
docker -v
docker build \
--label com.build.stage=3 \
-f ./backend/Dockerfile \
-t <dockerhub>/back_stage_1:build .
'''
sh "docker tag <dockerhub>/back_stage_1:build <dockerhub>/ack_stage_1:${GIT_COMMIT}"
}
}
The Dockerfile tied to this stage looks like:
#Using ubuntu as our base
FROM ubuntu:latest
#Install commands in ubuntu, including pymongo for DB handling
RUN apt-get update -y
RUN apt-get install -y python3 python3-pip python3-dev build-essential
#Unsure of COPY command's purpose, but WORKDIR points to /backend
COPY /backend/ /backend
WORKDIR /backend/
RUN pip3 install requirements.txt
#Run order for starting up the backend
# ENTRYPOINT ["python3"]
CMD ["python3", "-u", "app.py"]
Just a simple Dockerfile that installs the dependencies.
This step sometimes works fine but sometimes gets stuck.
The error that I am getting looks like:
Step 5/11 : RUN apt-get install -y python3 python3-pip python3-dev build-essential
---> Running in ba358993dc8b
Reading package lists...
Building dependency tree...
Reading state information...
The following additional packages will be installed:
...
...
0 upgraded, 135 newly installed, 0 to remove and 2 not upgraded.
Need to get 117 MB of archives.
After this operation, 390 MB of additional disk space will be used.
Err:1 http://archive.ubuntu.com/ubuntu bionic/main amd64 liblocale-gettext-perl amd64 1.07-3build2
Connection failed [IP: ...]
It just keeps giving me Connection failed error until I abort it.
When it works, it just successfully installs all packages and goes through the entire steps successfully.
I don't understand because it's too inconsistent and fails even though I did not change anything in the Dockerfile or Jenkins. I feel like it has something to do with some Jenkins' trait that I don't know.
Any help?