Damage to the white disc under the bobbin case usually happens in one of these ways:
1. The needle isn't all the way up in the needle clamp, so it hits.
2. The needle clamp is not tight and the needle slides down.
3. The needle breaks and the tip falls under the bobbin case and gets pushed into the spinning hook race.
Due to the unusual situation we are in, shipping is completely unpredictable. Amazon usually delivered next day prior to the lockdown. Now it's a week or more, or in the case of elastic shipped from China, never. I don't know the state of shipping in the Janome warehouse. If they are not shipping that is a huge factor. UPS, usually reliable, is having their own hard time. Recently we got a package of frozen yogurt treats intended for someone else. It was packed in dry ice, but was actually in-transit for 13 days. The dry ice was long gone, and even though we contacted the rightful recipient immediately, all was lost.
Regarding the aforementioned white disc, most dealers never change it. It's one of the easiest parts to change, second only to the needle, and it's cheap. Many technicians regard it as trim or window dressing, even though every stitch must drag across it.