Health Insurance Accidentally Cancelled

So today I found out that my husband’s health insurance was cancelled by the health insurance marketplace. There was no notice or warning and I only found out from logging into my husband’s health insurance and realizing it was inactive. I had recently reopened an old application through them for my daughter’s special enrollment period, my husband was also on the application, but I didn’t realize not checking his name under “who needs health insurance coverage?” would essentially cancel his current plan. It does not warn you that you are making any changes to active health plans. His coverage apparently ended September 1st, when my daughter’s plan started. He’s had this same coverage for 3 years and we were all caught up on premium payments, with $0 due. I opened a case with the marketplace, and they put it as an urgent matter because now my husband cannot pick up his life-dependant medication unless we pay out of pocket. They said usually in a case like ours you’ll get a call back in a few days, but it can also take up to 30 days. She also did say “if they accept your case” so now I’m worried that I really screwed up and he won’t have coverage until 2024. My questions are:

Has anyone ever had something similar happen? What was the outcome?

Isn’t it illegal for them to just cancel your plan without notice, even if it was from an action you took?

If we do have to pay out of pocket for medication, will the insurance company reimburse once the plan is active again?

Can they keep your insurance cancelled from a mistake you made on your application? I’m really worried he won’t be able to re-enroll until open enrollment.

I live in Michigan if that matters. Any reassurance is greatly appreciated.