Exceptionally poor penmanship is definitely a problem in my case, wherein some of my Latin-based English writing is sometimes done in such a scrawl that it almost resembles Arabic writing or Gregg shorthand.
[size=8pt]Yet when it comes time to read it back I always manage to do so with 95% accuracy. Although I often have to transcribe it when other people need to read it.
As for my personal journal, well, the underlying language is English but it's all encoded in A3byKA! (or "cyrillic", "Azbuka" for our non-Kodirovka Volapyuk readers; specifically Russian Cyrillic.) That I do manage to write legibly. I guess it's because I haven't been writing Cyrillic for as many years as I have been writing in Latin characters, and haven't yet found ways to make it into letter slop.