Sounds there may be an ERISA violation -- not my specific practice area, but you should contact federal Department of Labor (www.dol.gov), the agency that enforces ERISA.
Since it is part of your employment conditions, even if the insurance company is off the hook the employer, as Plan Sponsor and the individuals who screwed up are on the hook for any costs that accrue to you. I doubt that this would be considered a break in coverage but the insurer could try. If that happened the employer would be liable for your care. See what happens in the next few months to you or your co-workers. Also make a WRITTEN request for coverage docs with dates of coverage. If there are any problems after that, contact an attorney who is experienced in ERISA.