Shell Runner CICD stop working after update to GitLab version 13

I have been running may CICD pipelines on containerized gitlab runners for a while.
Updated the Gitlab solution to version 13 (from 12) last week and all has been running smoothly until shell running pipelines have been triggered.
None of the shell pipelines that before were running without problem are running now. The error pops in straight:
Running with gitlab-runner 13.6.0 (8fa89735)
on Shared Shell Runner 7iYAENX4
Preparing the “shell” executor
00:00
Using Shell executor…
Preparing environment
00:00
Running on c8958abcef93…
ERROR: Job failed (system failure): prepare environment: exit status 1. Check https://docs.gitlab.com /runner/shells/index.html#shell-profile-loading for more information

I have checked the link provided in the error but cannot see anything wrong and it troubles me that I have not changed anything in the environment but the Gitlab version.

Any advice please?