Dear X , below you'll find the last emails that I received from W. As you can see, the most likely explanation is a damaged optical fibre. The technician suggested we use a tool called fibre scope to examine the tip of the fibre. As far as I know, we do not have such a tool. Am I right? He also suggested we buy a fibre cleaner liquid in order to try and fix the problem. However, I believe that buying this product would require at least three months. Hence, it does not seem like a viable solution. Would you agree with me that the best possible solution would be to arrange a visit from the technician? Best regards, X.