Hi @Fintan3 ,
It does sound like a fault or hiccup somewhere that your bandwidth over the VPN feels like it is being constricted over time. On balance, your VPN provider has the best chance of determining where the constriction lies as they can test everything after you first hit their servers using your internet access method.
The service provider is contracted to provide you with internet access and your wife's data/evidence suggests that is present and ok. The service provider is not out of the woods because you've reported that your colleagues are fine which perhaps marks you as an unlucky person.
A naïve hypothesis is that the VPN provider is not properly load-balancing VPN users between servers but the fact your colleagues are unaffected argues against this. Perhaps one play may be to access the VPN using another device but you may not have another significantly different device hanging around. One play could be to deliberately generate a low-level of traffic going via the VPN link to see if the constriction still occurs (the simplest would be to ping some public endpoint or maintain a fixed 1 Mbps upload).
I guess the best play is to coordinate with your VPN provider to monitor your traffic as you simultaneously carry out a large download or continuously run online bandwidth benchmarks to see where the traffic is being constricted (obviously at such time as you notice a constriction).
