Are the whispers (waswas) that afflict a person, especially the waswas of intention in prayer, which leads to repeated attempts to form the intention and delaying the prayer, a sign of Allah's anger and His lack of love for His servant?

Waswas (whispers/obsessive thoughts) are an illness and an affliction from Allah, and they are not necessarily a sign of His wrath or a lack of His love. The best cure for them is to ignore them and pay no attention to them. When praying, say the opening Takbir (Takbirat al-Ihram) immediately after fulfilling the conditions, and do not exit the prayer due to the devil's whispers. Slight movement away from the Qiblah or the unintentional uncovering of a small part of the awrah (private parts) does not invalidate the prayer. Furthermore, it is not obligatory to maintain the intention throughout all parts of the prayer. The religion of Allah is ease, so do not be hard on yourself.