Internal Wall box C141? Red RX light flashing

Hello,

Had fibre installed about 6 weeks ago. After engineer left I noticed red RX light was flashing and he said that was normal.

I noticed the wifi was slow in some parts of the house but still usable at 20meg but had occasional "stutters".

Call was logged and the engineer replaced the router with a HUB 5. Mentioned the red light and he looked at the external box (he said it should'nt be on)and did something with the connector inside and the red light did not flash anymore. There was a flashing green now. 

Just had another engineer back to replace cable from external to internal box as the black  outer cable had come away from the external box exposing a white inner cable. The red light is now flashing again at about 1 sec intervals.

Can't find any info on the white box or what the status of the lights mean. RX flashes when doing speed test but the red light just keeps on blinking just the same.

Do I have a problem? 

Thanks, T