@Tanya Denton I manage 2 Tenants ( 1 in UK & other in Denmark), but haven't experienced that yet (or in last few days). is this happening to you specific or other Admins as well in your organization.
1. You alone are affected, then restart machine, and probably clear up cache (should fix it) , additionaly, ask another Global Admin to remove your permissions, wait 20-30 minutes. then readd the permissions to see of it works all good for you.
2. If multiple admins experiencing the same behavior, then best is to approach Microsoft Support and ask to have your Company Configuration Refresh (Full Sync) and RBAC Update.