Why it was added I can't say, but why they keep it on that list... the number of incidents at events involving ecstasy might be a reason (ecstacy accounts for nearly half of those), or even overall usage (NL leads EU on that):
The Netherlands has the highest last year prevalence rate of ecstasy of all EU countries.
Although the EU review says that, it only gives some numbers to compare for lifetime prevalence, in which indeed the NL with 8.4% is well above EU average of 2.9%; the paper also gives the last-year prevalence, but only for NL (that was 3.4%). All these [three] figures are for 2015.
Anyway, they also say this about the high occurrence of ecstasy-related incidents at events:
In 2014, the Monitor Drugsincidenten (drug-related emergencies) (MDI) of the Trimbos
Institute reported 3797 drugs incidents. In 47% of these cases ecstasy was used, in 19%
of the cases cannabis was used and in 11% cocaine-HCL was used. The number of
ecstasy related incidents has not increased since 2012, however the severity of ecstasy
incidents reported by First Aid Posts at major events continues to increase in 2014.
However, there were few admissions to hospitals for ecstasy (actually psychostimulants in general, they don't break these down beyond that):
The National Medical Registration (LMR) registered almost 2 million admissions in 2012, of
which in 538 cases drug abuse and drug addiction was the primary diagnosis. Of these
admissions, 14% these were related to cannabis and 16% to cocaine.
The National Medical Registration (LMR) registered 2938 cases in which drug abuse and
drug addiction the secondary diagnosis, of which 26% was related to cocaine and 25% is
related to cannabis. The most common primary diagnoses in these secondary diagnoses
were: accidents; intoxication; heart-disease; abuse or dependence on alcohol; diseases of
the respiratory tract; abuse or dependence on drugs; psychosis.
The LMR registered few annual admissions to general hospitals with psychostimulants as the diagnosis: 67 in 2012 as primary diagnosis and 196 admissions in 2012 as secondary diagnosis.
My quotes are from "A review and assessment of EU drug policy" (2016).
I looked at a Dutch MDI study, but it doesn't seem to get into details as to what those first-aid incidents involved specifically/typically in terms of health/symptoms. But it does have this combined graph of problems by drug, and this reinforces the impression that the main negative impact of ecstasy on users seem to be of the first-aid-required kind.

The "ziekenhuizen" bars are hospital admissions (primary/secondary reasons, I think); EHBO is first aid. The other bars should be self-evident (police arrests and ambulance need). They later have a breakdown of comorbidities for the ecstacy first-aid incidents. My google translated version of that says that in 45% of cases alcohol was also involved, and that 32% of cases also involved another illegal drug (i.e. a "cocktail"); this comorbidity data is only for 2016, which is probably why the "cocktail" figure is different from the 8-year cumulative data in the graph above.