Prime video connectivity error code 35

Prime video was working and then stopped a few days ago with above error. Have unplugged everything , reset, deleted app etc to no avail. Seems to be common issue! Even Amazon could not figure it out..

all other apps work fine and internet is excellent 

any ideas? 
thanks…………

just discovered that if I change the network setting in Roku to 2.4 rather than 5 ghz it will work!

the other apps worked with the 5 ghz but not Prime video. Does that make any sense and is there a way to have prime video  work under 5 ghz?