Inconsistent word skipping

assalamu 'alaikum. the vocab challenges are supposed to automatically skip words that are unfamiliar. however, they have been skipping words that i have learned. i completed Surah Maryam (100%) seven days back. today, when i came across a verse from it in a vocab challenge, the system skipped four words, despite my familiarity.

additionally, some common words are also being skipped in certain challenges but in some challenges we are allowed to do them…? e.g., ما، لهم ، هم etc. this is frustrating.