Worst case usage determines what information is subject to GDPR, but actual business use-case is what determines what data you are allowed to collect.

IP addresses are subject to GDPR, but that just means that you have to have either a legitimate business need for keeping them or to have the user's consent to keep them and you need to disclose to the user that you are keeping them and for how long.

You probably do have a legitimate need to keep IP address logs for some period of time to allow troubleshooting and possibly for a longer period of time to allow for fraud detection. As long as you are disclosing to the user that you are collecting that information and are abiding by the retention period that you are disclosing to users, then you will be allowed to collect logs of IP addresses.

Your intention and how you actually use the data are critical to an entity's compliance with the GDPR. If I am only using IP addresses for legitimate purposes of monitoring/protecting my network then that is very different to using IP addresses to assist in my tracking of users for advertising purposes for example.

The classification of data of personal data is likely beyond dispute but you are then under obligations on how you actually make use of that data.

Entities should have in place relevant protective measures to ensure that if you have only collected data for a limited purpose, it should not be used for purposes beyond that.

In my experience of having lived all my life in the EU and mostly in 3 countries of the union, all law enforcement here is about intent, unlike the US for instance (as far as I read online ofcourse, like the Nintendo copyright case linked here a week ago). Copyright, drugs, bankrupting your company etc, judges look at intent not literally what the law says. So this will not be different. Nothing will change if you are not trying to actually go against what the law intents to protect.

Mens rea (i.e. intent) is part of common law criminality (along with actus reus, which is the actual doing of something illegal). The United States, having its legal system derived from that of England’s (and thus being a common law legal system), absolutely requires intent when considering whether or not someone or some organization has committed a crime.

I’m not familiar with the referenced Nintendo case, but mens rea is usually only considered in criminal cases. Unless you’re prosecuting someone for illegally downloading copyrighted material or some such thing, intent wouldn’t be considered (it can increase liability in civil cases, though).

Now that you mention it; I do see it in crime shows. But the case I mentioned was about if a Nintendo modchip could be used for good or only for evil according to the EU while the US court just yelled copyright infringement and put some hacker in jail. Those are the cases we read about in the press over here and most people find it ridiculous over here to go to jail (aka ruin lives) over something as small as copyright infringement. Courts agree as they usually mostly slap on a fine based on the intent.

And it even gets more interesting: The question is not if you can identify a user by merging your different data sets. The question is if you can identify a user if you merge one of your data sets with any other data set, even if this set is currently not in your possession. (This can happen if the provider is able to mach IP addresses to personal information.)

Intent comes into play when you determine the appropriate processing basis; for eg preventing abuse, the basis isn't consent and therefore consent is not required. So GP is partially wrong. If your intent is to use the data for marketing purposes, then you are much more likely to require consent. See LI balancing tests.