Does refraining from visiting the paternal uncle and cutting ties with him after his false complaint against the father constitute severing kinship ties, even though the father did not request that?

Severing ties of kinship is a grave sin. The uncle's injustice towards the father does not negate the uncle's right to maintaining ties. For the one who truly maintains ties is he who connects with those who cut him off. Cutting off ties with a relative and ceasing to be kind to them without a legitimate Shar'i excuse is a forbidden severing, and it becomes a major sin if a person cuts off what the relative was accustomed to from him in terms of connection and kindness. It is obligatory to maintain ties with the uncle, even if he wronged the father, along with advising him and warning him of the consequences of injustice.