Bondage and safety worry - please offer advice

Hi all, I’m new to posting here, though I’ve been enjoying rope bondage for a long time. I’m searching for an online expert or community that can address one of my safety worries in bondage, so hopefully this is the right spot. If not, any pointers to helpful blogs, sites, or forums would be much appreciated. Here’s what happened… A few years back, I had a partner who was new to bondage and BDSM generally. She wanted to give it a try, so I connected her with a dom I knew well for his experience with rope. From what I know, he’d tied hundreds of people before, and I’ve never noticed issues with his technique, safety measures, or attentiveness (even in public settings). He put my partner into a diamond chess harness, and the quick session went smoothly. Afterward, she reported neck pain, specifically where part of the diamond harness rests against the back of her neck. At first, I didn’t link the pain to bondage since I hadn’t come across such injuries before. Later on, she started having headaches and bouts of severe dizziness that persisted for months after the incident. She saw several doctors who couldn’t explain it until a neurologist suggested that the rope might have awakened a dormant condition called Arnold Chiari malformation at the back of her brain. Essentially, due to tissue weakness in her neck, some nerve endings extend backward where they shouldn’t (I know this isn’t perfect medical terminology, but I’m not a doctor and don’t fully grasp all the details). Has anyone heard of this? Do you think rope could have aggravated it? In reading through various BDSM forums and blogs, I didn’t find much mention of this. Clearly, we’ve read that rope shouldn’t be wrapped tightly around the neck, particularly the front and sides to avoid asphyxiation or nerve damage, but I’d never heard of a diamond harness causing this specific issue. I’ve worn this harness several times myself and felt no physical threat from it. Was it just an odd occurrence, or something more? I’m ready to accept full responsibility for my actions and admit I may have erred by letting my partner into that situation. However, since then, I’ve done the harness many times (along with other ties) without any problems. My former partner is certainly upset about this and hasn’t tried bondage or BDSM again after that point. Thanks in advance for your advice, The Concerned Rope Guy