Columbus MIB 2.5 - Poor Radio Reception?

Hi all,

I have a Columbus 2.5 retrofitted in my 2015 Octavia which worked perfectly to start with.  I've recently noticed the FM and DAB radio reception have become very poor.  I can get a signal but it's very intermittent, cutting in and out when on the move in areas of good reception. 

I've checked the AM/FM and DAB antenna connectors on the rear of the head unit and they appear to be fine. 

I have installed a front and rear dashcam which I thought was to blame but if I completely disconnect the dash cam power it makes no difference at all. I also installed a genuine SKODA rear view camera but I've also disconnected that and no difference. 

I believe there is a small inline signal amplifier in the rear pillar near the antenna. Has anyone ever seen one of these fail? That's the only thing I can think of at the moment.  There are no other new electrical devices which could be causing interference and nothing else has changed.

Any ideas welcomed!

Thanks.