There is theoretical limit of 256 certificates per Virtual Service.
This is because the configuration entry holding the names of the certificates has a maximum length of 1023 characters. If we assume that the certificate names are two characters long, plus the .pem file extension and spaces between the names, this gives 256:
file name (2) + .pem (4) + space (1) = 7 characters:
1795/7= 256 total certificates with a 2 character file name
If you are using longer certificate names, this limit will be lower.