Can cause by increasing Premption drops if you have that enabled and you have SIMs of multiple classes issued in your network then the system may drop a call of lower class sim to accomodate for call_setup of a higher class sim.
Also during high traffic there is increase in system’s internal noise floor that causes increase in drops.
Also during high traffc cells are congested and certain handovers get delayed or rejected due to congestion which results in call dragging and dropping or attempts to non best serverer neighbour causing increase in Handover failures resulting in increase in DCR.