Answer:
1. Changes in network topology or system configuration might bring security-related challenges. For example, adopting a new system configuration which is low in cost but also very new in the Industry might be vulnerable to the existing security.
2. New products or Services which are delivered to either the Internal/External users might be prone to security issues.
Let say a product 'A' has been launched by a company 'X' and for testing purpose it has been given to the internal users. Now as this product 'A' is a product of 'X' itself it will be allowed to carry in the official premises and if some user tries to hack this product and can make the product potentially harmful w.r.t security.
3. Consider a scenario where there is a change in management & team, the team members which were thoroughly responsible for Security kinds of stuff are dissolved into different teams. Also new members are hired for the team. Now, since the new members will need some time to get adapted to the Business As Usual things there are high chances of a security level not maintained as it was earlier by the old guys. This could be due to undocumented things in the organization or due to lack of Knowledge Transfer to the new joinees.