Yamaha Steinberg FW driver Issue iMac MR816csx

Yamaha Steinberg FW driver keeps changing to 'In Built 'on my iMac.

4GHz Intel Core i7
Running OS Sierra.

Screen locks up …shuts down… reboots with 'Built In" entered in the Asio driver box.

The Yam Stein FW is still available and I just remove the ‘Built In’ and enter the Yam Stein Driver…reset the connections and all is well until the next ‘episode’ ( about 2 times an hour)

I really like the MR816 csx and hope that that is not the problem.

Any help would be much appreciated…hope I have explained it well.