(Sorry in advance for the wall of text, and for further derailing).
The comic goes on hiatuses with a great degree of frequency, entirely unannounced and unexplained on Webtoons. Alongside shorter and shorter chapters, and art that has degraded by several degrees. Also I think fans were miffed about the promised Halloween special never being delivered.
Also after a particularly pivotal moment of the current season, it went on hiatus for SEVEN weeks without a word from the author on Webtoons, just said "Lumine will be back next week!"... for seven weeks. I likened it to the Yellow Jacket Riots at one point on here, but the seven-week hiatus was like the London Blitz in the comment section. I was frustrated myself, but people took it about seven degrees too far and acted like uncivilized rabid animals.
Nowadays it's split pretty badly between people who are fed up with the author's lack of any form of communication and perceived updating whenever she feels like, and die-hard fans. So there's a ton of bickering between the two sides. It being a featured comic adds rhetoric that the author doesn't deserve to keep her spot if this is how she acts, especially since many other comics work hard and never get it, and other featured comics go miles above what Lumine does nowadays. Lack of communication I think is the worst offender.
TL;DR: Very inconsistent updates, a complete stone-walling from the author on the website. Shorter chapters, much lower-quality art, and a seven week hiatus on a massive cliffhanger, on a featured comic. Stonewalling is making people voice their anger.