Our Book Club's "No Spoilers" Rule Backfired On the Worst Book Possible

We started a strict spoiler ban 4 months ago. Everyone agreed. Then we picked The Silent Patient for our March meetup at the library on 5th Street. Halfway through, two members admitted they hadn't finished it. So the discussion turned into people trying to describe plot twists without actually saying them. One lady kept saying "the big event" and pointing at the ceiling. Nobody knew who she meant. We argued for 45 minutes about a character motivation that gets fully explained in the last 20 pages. In the end, we had to redo the whole meeting the following Tuesday. Are we the only club dumb enough to ban spoilers on a thriller? How does anyone else handle books where the ending changes everything?