EX6120 AC1200 isn't working properly

Afternoon all,

Background 

I have had an engineer out several times to investigate the 'line' and ensure my internet is working. The line is now fine, bios reports are great and a new router from Now Broadband 'The Hub 2 is an 802.11ac Wi-Fi router' just be certain.

Current situation 

I purchased the EX6120 AC 1200 to provide high quality internet boost in the conservatory. So far we have acheived the following:

- All lights green

- Signal is full

- Firmware is uptodate 

- No error reports etc are being recieved 

- Factory resets etc have been tried 

Problems are as follows:

- Internet quality when connected to the extender is mostly a failure 

- Games struggle to connect, speech on simple talk systems like skype and Discord also failure the quality check alot. I can hear my friend most the time without quality issue but to them, my speech is broken and delayed 

- Overall, there is barely enough solid internet consistency coming trhough for it to be reliable 

Help needed 

Please provide some steers how I can solve the above. When connected to main router internet is fine but signal isn't great so can drop off. The ext should easily be able to execute my simple needs. I don't want to just buy a boss type router when the ext ought to be working 

Thank you and god speed