I’m suffering from this currently, my thread is here: Excel Reader via Sharepoint Connector Broken following 5.1.0 Update - KNIME Extensions - KNIME Community Forum
This is a fairly serious bug. I am royally annoyed having upgraded to 5.1, found this bug that has wreaked havoc on my workflows and found the new visual interface pretty rubbish anyway (I have switched back to Classic)
My workaround is to remove all instances of the Sharepoint connector and write to a locally-sync’d version of the Sharepoint as if it were a folder, and then let the Sharepoint service in Windows upload the changes to the cloud (rather than the proper way, writing to the cloud and sync’ing the changes down to local level).