Ethernet & wifi fails diagnostic tests

Ever since we’ve had our install, out networking has suffered from intermittent internet loss, watching any streaming service, BBC Chan 4 etc will stop playing several times in one evening & start to buffer, despite being connected via Ethernet & have never had a problem before. 
I discovered the hub 5 was showing a failure’s for Ethernet & WiFi on the internal diagnostics in the Hub 5 .
So last week we got an engineer in who replace an external connection & internal as we still had the split in the coax that used to go to our lovely V6 box , (stuck with the crappy Streaming puc).  Plus a replacement Hub 5 but the problem remains, in fact I think it’s even worse, internet speeds are now lower, the engineer replaced an attenuator to control the upstream & downstream signal better but I am wondering if this was wise as all the internal connections used to work fine. Now I’m reading about this firmware Ethernet bug on the forums could this be the cause of our problems? We do have some Ethernet hubs splitting the signals . It really is frustrating to watch TV streaming with the quality going up & down or stopping.