Are You using Metadata columns hidden field internal name ?
for example Column name Would be " TaxonomyField_0 "
to get the metadata columns display name, follow below link
Yes, I tried using internal name of metadata column and also TaxonomyField_0. But didn't work.
As mentioned by you I tried to use guid of the column, but no luck.
Try the other action - "Web request". Using it you can provide credentials (https://help.nintex.com/en-US/O365/#o365/O365WorkFlow/WorkflowActions-INT/WebRequest.htm%3FTocPath%3...), so no such issues should occur.