This entity can allow a 3rd party service to access these logs so that 3rd party can do whatever needs to be done if it is within the reasons the entity gave for having the data.
What neither can do is go use that data for anything other than the said purposes.
And if the given reasons are gratuitous and somehow the regulators notice, expect to get a nastygram and have to comply or face fines.
Basically what you can't do is collect data for longer than you have a legitimate need for, or cash-in and sell data you've collected. Basically, all said and done, just don't be sleezy and you'll be ok.
If your angry ex is hired by a regulator you’d appeal it but there’s no reason to think that’s a common problem.
Have you even read the legal text you are complaining about?
https://gdpr-info.eu/art-6-gdpr/
> Processing shall be lawful only if and to the extent that at least one of the following applies:
Consent is one:
> the data subject has given consent to the processing of his or her personal data for one or more specific purposes;
Here are all the others (see especially the last one):
> processing is necessary for the performance of a contract to which the data subject is party or in order to take steps at the request of the data subject prior to entering into a contract;
> processing is necessary for compliance with a legal obligation to which the controller is subject;
> processing is necessary in order to protect the vital interests of the data subject or of another natural person;
> processing is necessary for the performance of a task carried out in the public interest or in the exercise of official authority vested in the controller;
> processing is necessary for the purposes of the legitimate interests pursued by the controller or by a third party, except where such interests are overridden by the interests or fundamental rights and freedoms of the data subject which require protection of personal data, in particular where the data subject is a child.