I think the real problem is not just that the plot isn't going forward - after all, this is a tournament arc. It's for having good fights and introducing characters.
The real problem is threefold:
1. Too little of the characters we're getting to know will matter at all
2. Too few of the fights we've seen so far have been very interesting
3. Of the characters who will definitely matter there are some major flaws
To elaborate:
1. The general ability level of the class we're in seems really weak. Every single time Shim Ha-Min's been in a fight he's utterly crushed his enemies (barring the time where he wasn't able to KO the other guy and only got a unanimous point decision); he's also significantly below Maria. Against the class's best striker the MC nearly went the distance even though he had maybe a month tops of training. Once he gets a little better he's going to absolutely skyrocket with the power of his eyes. That means those three are miles above the rest of the people in the tournament, i.e. the people with whom we've been wasting 20 chapters. This is a tournament that eliminated the MC in the first round, meaning that there's fantastic room to have a real mystery as to who will get to the finals!
But there is none, Maria and Shim Ha-Min were introduced as the strongest people in the class and they are, getting to the finals with zero difficulty each. There's no equivalent of the dark horses in Kengan or the carnival of colourful characters in YuYu Hakusho. The tournament is purely down to Shim Ha-Min V Maria, which we're only just getting to after 25 chapters. They were building one up for Shim Ha-Min in terms of Eul-Sol, but she's booted in the most embarrassing way possible in the most baffling decision in the manga, one of its more impressive side characters sacrificed to hype up one of its worst. What's odd is that Ha-min seems to have some trouble with actually KO-ing the random bowlcut guy, so it's not like he's some sacred cow that can never be touched. The author just didn't want to have him fight against the only non-main character who was getting any degree of momentum. For some inexplicable reason.
We spend half a chapter looking at the sambo guy who doesn't take his responsibilities seriously enough. That's great! He seems like a fun character. But what's the point of building up his byronic status just to have the actual fight be over in a single page? No look at how his false confidence crumbles? Or how he puts up a brave effort anyway? So we've wasted half a chapter characterising a random jobber for no payoff in the moment and none going forward because he will never matter.
I only mention this one because it stood out because it was relatively good by this series's standards. I really remembered that character, which is more than I can say for 80% of the side cast.
2. Since this tournament arc began we've seen maybe three decent fights. The Capoeria/Takkeyon fight, Eul's first fight and the Karate girl's fight when she loses. Every other fight has been a massive squash or has just been two characters beating on each other with no distinctive style, flair or tactics. Even if you want to build up characters as strong, having them win fights even when they're not using their strengths makes the story feel like it's operating off of DBZ rules. For example, Maria's used submissions maybe four times in the entire manga, despite her main style being BJJ. Every other time she's fought she's blitzed her opponents with pure strikes. Not only is neither character pressed so we can see how they handle under pressure, Maria's opponents can't even force her to use her main tactics.
Even those three good fights have significant flaws. The first ends rather anti-climactically, the second is rather short and only good for that one amazing panel, and the final one, while emotional, doesn't really bring anything to the table in terms of uniqueness or choreography.
So in a manga, called fight class 3, during its tournament arc, the vast majority of the fights suck. That is a problem.
3. Currently, there only seem to be three characters who matter in the entire tournament. One of them is the MC, who was taken out really easily, but the fact that he was able to see all the shots coming from the karate girl imply that he's going to get a lot better really fast and completely outpace everyone not called Maria or Shin-Han. The problem is that the MC, Maria, and Shin-Han all have glaring flaws.
The MC has a pretty bog-standard motivation and has no real interesting character moments to speak of; also, how easily fighting comes to him is a constant niggle (things like throwing a punch perfectly the first time despite never practising it are just obnoxious and unnecessary). He's just kind of there.
Maria is waaaay too psychotic to root for. After the ultimate hero fight she went from "troubled hero" to "sympathetic villain". I'm actually fine with her beating up the MC in his house because we saw the PTSD trigger go off; against the Ultimate hero guy even though he was chatting shit she could have just broken his arm or something instead of going out of her way to nearly kill him. I would broadly say that there's at least potential here, but at the same time there's so much page space wasted hyping up a character we already know is really good, which also irritates me. We don't need chapter after chapter of Maria dominating her opposition; you'd think the author would know this by having her tournament fights take place offscreen but he still crams her in the flashbacks.
Shim Ha-Min is just boring as fuck. Despite making it all the way to the finals and getting a multi-chapter flashback, he is essentially still the guy we were introduced to. He likes Maria and he's really strong. Those are his only two character traits. His backstory does nothing to expand on that.
These points are all interlinked. The weakness in the side cast brings into focus the flaws of the main trio. The weakness in the side cast is partially because they suck in fights, and they suck in fights to hype up Shim Ha-Min and Maria.
In short, the plot's going nowhere, the characters are either boring, fodder, or both, and the fights need improvement. Could the manga still make a comeback? Definitely. Will it? Only time will tell. But one thing's for sure, it's making a comeback from a rocky, rocky second arc.