The course teams cannot fix possible bugs, I am afraid. Please report bugs to Duo - https://support.duolingo.com/hc/en-us/articles/204728264-How-do-I-report-a-bug- If you use the app, first check that you have the latest version.
Is the preposition 'i' before 'fi' here a long or a short vowel sound? Based on the Wiktionary pages for 'iddyn' (and 'iddo' and 'iddi'), it is a short vowel (I always pronounce Welsh words as the North Welsh do to remember which words are spelt with 'y'/'u' and which ones are spelt with 'i'). However, that could just be because it is part of a longer word.