If you have a wildcard certificate (for example *.randomhacks.co.uk) you might need to install it on multiple servers which host the different subdomains.
Basically, don’t rekey the certificate for each server just copy the same keys and certificate files across all the servers. If you rekey the certificate each time then you will invalidate any certificates which used the old key.
Typically you would need to copy these files:
Note: GoDaddy let you use their wildcard certificates across an unlimited number of servers. However if you are using another certificate provider you might need to check that they don’t have a limited.