Jenkins pipeline stuck on Build - jenkins

Question

I have a few services running on a Kubernetes cluster on ibmcloud and I use Jenkins to deploy these services.
So, until yesterday everything was working fine, but today as I tried to re-deploy my services 2 of them got stuck on "BUILD", freezing Jenkins, and the only way to get Jenkins to work again was by running "systemctl restart jenkins" on the remote machine where jenkins is installed.
After restarting Jenkins I went into the failed build
The end of the console output was:
[Pipeline] }
[Pipeline] // stage
[Pipeline] stage
[Pipeline] { (BUILD)
[Pipeline] sh
+ yarn build
yarn run v1.16.0
$ yarn clean && tsc
$ rm -rf dist/
Done in 7.25s.
[Pipeline] sh
+ yarn build:webpack
yarn run v1.16.0
$ webpack --config webpack.config.js
Resuming build at Fri Mar 13 23:00:58 UTC 2020 after Jenkins restart
[Pipeline] End of Pipeline
Global Slack Notifier try posting to slack. However some error occurred
TeamDomain :
Channel :build-info
Message :
java.lang.IllegalStateException: JENKINS-50407: no loaded shell in CpsFlowExecution[Owner[isa-v2/user-service/2:isa-v2/user-service #2]]
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.run0(SandboxContinuable.java:35)
at org.jenkinsci.plugins.workflow.cps.CpsThread.runNextChunk(CpsThread.java:185)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:400)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.access$400(CpsThreadGroup.java:96)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:312)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:276)
at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$2.call(CpsVmExecutorService.java:67)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:131)
at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:28)
at jenkins.security.ImpersonatingExecutorService$1.run(ImpersonatingExecutorService.java:59)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)
Finished: FAILURE
I've tried to delete pipeline and create it again, updated jenkins but still no luck.
Truth is I don't really know much about Jenkins and I'm getting kind of desperate here! :x
It was working fine yesterday, no code was changed, no Jenkins configuration or pipeline changes eithe. It just seems to have started out of nowhere.
Could someone please help me figure out what is going on and how to fix it?