As I said in an earlier post, remote commands require a response from a Cox server. If you're having a signal issue, the response may not be received. That's why your remote doesn't always work. Was it a contract tech that said the signal from the remote may be the problem?
Do you know any of your neighbors well enough to ask them if they're having similar issues in the evening hours? Because it only happens at night, it sounds like a main line issue that could be affecting your neighbors too. If it is, ask them to contact Cox, if they haven't already, That could help Cox identify the problem which could result in it being escalated and the solution being found.