Have you noticed performance issues with the Windows Event log service when a log file size is set to a few GBs? I'm not sure if NXLog is a factor, but perhaps it may sometimes struggle with large event logs?
We have our security event log set to 4 GB size on all servers. I've noticed that there are high CPU and RAM utilization on 5 or 20 minute cycles. The process using the CPU is svchost EventLog. Derived from using Resource Monitor and running: