Slow broadband and work VPN keeps dropping out

[#1]

One further comment, following @krusty 's post - check both cables, the one from the ONT>router and the one router>test device.

[#2]

Yup.. It could be switching from 1gbits to 100mbits ...

[#3]

I'm on the 300mbps package

[#4]

I encountered a similar issue and initially suspected the cable was the problem since I was only receiving 90 MB speeds, I switched on the Wi-Fi and noticed an improvement to 120 MB. Consequently, I decided to replace the cable. However, during the process, I turned off the Ethernet connection and then re-enabled it. This has resolved the issue and now I’m experiencing a full 500 MB speed. I suggest you try turning off your Ethernet connection and then re-enabling it. Please note that it was on a Mac.