Did they site any incidents of problems with cross draw or shoulder holsters or were they banned because they are harder for the instructors to deal with safely?
The reason I ask is that I see the SERPA "safety problems" as an extension of that issue... instructors don't want to (or know how to) teach or monitor its proper use, so they ban it.
My source
cited an injury and a non-injury discharge related to the use of the Serpa. With those circumstances presently before the training staff, and following the required incident reporting of unintended gunshots, their Risk Management folks made the determination. Perhaps less of a concern with the private sector training vendors, it is of considerable importance to this governmental venue. A Federal agency has also prohibited the holster from use for similar reasons.
In this instance it is not the case that they can't teach it or don't know about it, but with other, more problem free alternatives available, why risk someone else's (the user) safety when established circumstances can reduce that risk.
I have personally seen one retention mechanism break on the Serpa and witnessed another have a screw lose it's retention of holster to belt slide. My correspondents have provided other circumstances of the retention screws pulling through and loose of either the paddle or belt slide. My trainees are not prohibited from using the holster, but policy has established that they are responsible (and documented in agreement) for any quirks or problems that cause a safety violation or keep them from passing a qualification course. It is the only holster that is addressed by name for this problem.
I'd grant that some of the problems are user induced, but would also say that even "monitoring" students is not going to prevent a problem exacerbated by stress and circumstance.
The manufacturer remains pretty silent about their product, and in several iterations of their product and it's instructions, have yet to mention a word on proper use and technique. I'd suspect they understand that technique is important, given the video footage they've produced, but they are publicly mum.