I’m also working on bolt investigations at the moment. As FEAnalyst mentioned I would first go with pure Tie in bolt head and connection between the parts. When this case is working switch one by one from Tie to contact (first start with the bolt head). From my experience it can be helpful to change Tie adjustment of the fixed bolt end from default to a defined position tolerance like > 0.1. Especially if you have a coarse mesh. Is your model compareable to this model approach here?: https://prepomax.discourse.group/t/bolt-pretension-model/2037/5