Antonym of 涨粉 (zhǎngfěn, gain followers). Both work as transitive-style verbs even though Chinese morphologically treats them as verb-object: 掉了一万粉 (lost ten thousand followers) is grammatical.
memory
粉 (fěn) — short for 粉丝 (fěnsī, 'fans', borrowed from English 'fans' via the noodle homophone). 掉 means 'drop'. Picture follower numbers ticking downward.