The Multi-line Text metadata specifier is not able to be set in a Blueprint. This means that text variables that are created directly inside of a blueprint cannot have this specifier set and cannot have line breaks.
Workaround: Create your text variables in a struct, where this metadata specifier is available
This also occurred in 4.13
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-42147 in the post.