Hi @lone_Ranger
Is it an issue with only Multi Line text field?
Are you able to access any other Content Fragments which has different type of fields? If it's global issue, please verify whether you're using latest core components or not.
I had similar issue with experience fragments and it got fixed after installing latest core components package. you may try installing latest core components and see if that helps on your local.
btw, Which version of AEM & core components are you using?