It is INCREDIBLY frustrating to REPEATEDLY go through the processes of (1) complete the "Contributing Handwriting" feature multiple times, (2) add Custom Words to the Personal Dictionary, and (3) when a red line appears tapping on the redline then "More" --> "Add to Dictionary" --> then complete the "Add Custom Word" field AND THE RED LINE REMAINS after tapping Save. Please know this REPEATED experience has frustrated me to the point of looking at alternative handwriting recognition apps or go back to keeping a paper journal.
I'm in a professional occupation where keeping a journal is essential, and repeatedly going through these steps is causing me to reconsider the REAL value of journaling on my iPad using Goodnotes.

NOTE: I've intentionally and hopefully thoughtfully used capital letters (i.e. shouting) in the above comment to stress how frustrating this is (and in lieu of cursing which helps neither of us). Please take this comment seriously.