It found the problem appears general to all collections when 'PLAY’ing, but doesn’t occur when 'REVIEW’ing.
Half points are awarded if the single letter hint is used, you switch to multiple choice, or the sentence is played before it’s actually ready for review.
Given you mentioned that this doesn’t seem to occur when playing sentences ready for review, I suspect it might be due to playing sentences before they’re actually ready for review. And given the number of sentence you’ve played for Spanish looking at your profile, I suspect you might not have any entirely new sentences left to play, which is why when playing “new” sentences the algorithm is falling back to sentence not yet ready for review ordered by when they’re next be ready for review.
Curious to hear if you think the above might be the case. The rationale was to try to reduce cheating by mastering a sentence early and then continuing to re-master it early to rack up points.