Shared calendar disappeared

Hello

My husband and I share several icloud calendars for the business we run. Most of them have been created from his Apple ID and shared with me, and of the 8 we have, 1 particular calendar has disappeared - BUT ONLY when signed into iCloud calendar (from either my or his Apple ID) on our PC (which is not a mac). It still appears on our iPhones and iPads, just not on the PC. We have tried signing out and signing back in on both IDs. We have tried deleting that calendar on my ID and re-sharing it with me. It's one of the essential calendars as it shows the appointment slots that are not available, so really need to have it shown on our PC, as that is what I use in my reception to book our patients for their next appointments. Any ideas how to fix this problem?