Won't stream without crashes

On what streaming device?

What does Netflix say about the problem?

Have you run any of Netflix's network diagnostics?

ATT Fiber 6 modem/Router

Smart TV crashes, Dumb TV is OK using 4K Blu Ray

Netflix said in a chat to reset all equipment (telling me how to restart viewing).

I want to know HOW TO PREVENT CRASHES

Cannot find any Netflix diagnostics

Update: I eliminated the curve in the Fiber cable where it is inserted into the modem/router. No crashes last night.