Digi Portserver TS 4 HAZ MEI keeps crashing

I have a Digi Port Server TS4 HAZ MEI it crashes at least once a day. It is setup as Rs-485 2 wire industrial automation modbus RTU Slave. I have tried several setups and it still seems to crash. The only way i can get the unit back online is by resetting via the web browser. I am polling using kepware and poll about every 5 minutes. Any ideas why the unit crashes so often?