The main issue I've found is the manufacturer's implementation. They range from okay to barely meeting the minimum standards.
One thing that always annoyed me was the time stamps. They're mandated by the standard, so there's always a timestamp, but it's often useless. For example, it seems some scanners don't get their time set, over the network or otherwise, _ever_, so you might have a bunch of scans performed a few years ago on scanner A with an accurate timestamp of say 2017, but in a new scan from last week that was taken by scanner B, which hasn't had its clock configured properly, it reports a date closer to the start of the unix epoch rather than 2020.
Of course some of this is out of the manufacturers control, but temporal data is critical to analyzing changes to patient over time. I think this is one area where the DICOM standard couldn't be a bit more strict with a lot of positive impact.