PlanetZ forums - scopeusers.com

No matter if it's someone's herd of bots or even payed accounts, attacks like these also bring some effort for the attacker. So there usually is some goal, to get some payoff. As there's no shop with wallets, no data for identity fraud, I don't see a monetary motivation. Even if someone hates all scopers, it's hard to believe he keeps up attacks over such a long time.
Many years ago, some people scanned IPs "close" to an interesting site (e.g. webshops, pr0n) , to find a way to access its data by some backdoor.
Is it possible, that your site is just part of an "interesting IP-range" ?
Do the "knocked ports" show a pattern, which adresses a certain type of host ?

There are only 4 ip addresses for all 40 accounts. Its domain specific to the point where it’s only the forums subdomain, not even the root domain

I also still host some very old gaming forums that have been around just as long if not longer, they do not get any of this traffic. Same forum software so it’s not people trying to hack the forum because of the type of forum etc.

Believe me, it’s been going on long enough that I’ve certainly come to some conclusions and it’s not random.