Update: I have to rectify my initial “complaint”. Whilst the issue seems to have been caused by the columnar backend - please note that I took utmost care by resetting, regenerating saving the workflow, closing and repoening - the issue was caused too while back testing again.
As follows the test workflow but w/o the sensitive customer data (shared via PM with the Knime team). Please note that I possibly tracked the issue down to lots of string data being present (1.3 GB) while investigating about a general Knime instability: