I believe your  vcenter machine is deployed with ip deployment

if there is an IP deployment, the PNID is set as IP address. You have two options

1.Change pnid to FQDN instead of ip and replace with same cert - Changing your vCenter Server's FQDN - VMware vSphere Blog

2. Include ip address in Subject alternative name and proceed to change cert (keeping pnid as ip)

thanks,

MS