I have discovered that the User Picker control used to select users for various components in Jira Service Management is not returning any results.
My account is the project administrator and I'm able to browse users elsewhere but the picker itself never seems to function, even if I try to select myself.
To better illustrate this I have captured an example when selecting the Project lead. Note that my own name does not appear either and that I'm the project administrator (and organization owner).

I suspect there is something wrong in a permission setting somewhere but I haven't been able to find it. My system started out on Jira Server and was migrated to Cloud so that may have been the cause.
Any pointers would be appreciated.