MS510TX Multi-Gig Switch - Speed Issue

MS510TX Multi-Gig Switch - Speed Issue

Hello all - I wonder if someone would be kind enough to offer me some help. I have owned an MS510TX Multi-Gig switch for a couple of years (it's running the latest firmware) I have 2 workstations with 10Gb network cards attached (one connected to the 10Gb RJ45 port, and the other to the 5Gb Rj45 port), together with a Synology NAS on the 10GB SFP port. All network cables in use are CAT7 and CAT8 spec. For internet access I have a TP-Link Archer C2300 Router (it's running the latest firmware) connected to one of the 1Gb ports on the MS510TX. The Router WAN connects to a Virgin Hub 3 configured to run in Modem mode. The MS510TX is set to a fixed IP, with the TP-Link Router assigning the other connected devices their (fixed) IP addresses via DHCP. QOS on the TP-Link router is set to standard - 999mb upload/999mb download. I subscribed to Virgin Media's 600mb service and was getting a 600mb download connection to the Internet as standard. All was cool!

I was offered an upgrade to their 1Gb service last week and was sent a new Hub 4. To save reconfiguring everything I disconnected the Hub 3, put the new Hub 4 into Modem mode and fired everything up - that's when my issue began. The first thing I did was run the desktop version of speed test and noticed my main workstation was only giving me 650mb max download speed. To ascertain why I wasn't getting a download figure nearer 1GB, I took my MS510TX switch out of the loop and connected my main workstation directly to the Archer Router LAN 1 port. I ran speed test again and saw an immediate improvement - I was now getting 880-900Mb download speed. As soon as I switch back to connecting via the MS510TX the speed drops to 650Mb. (Although I may be wrong?) I'm assuming the MS510TX is causing the issue with the significantly lower download speed.

(Connection map)
Netgear MS510TX Multigig Switch (port 09 10Gb RJ45) <=====> Workstation 1
(port 08 5Gb RJ45) <=====> Workstation 2
(port 10 10Gb SFP+) <=====> Synology NAS
(port 01 1Gb RJ45) <=====> (LAN 1) TP-Link Router <==WAN==> Virgin Media Hub 4 (1Gb)

Can anyone explain to me why integrating the MS510TX and connecting my devices via it is causing such a degradation in Internet download speed? Maybe there's a setting on the MS510TX that I'm unaware of that's causing the issue? I'm fairly Tech Savvy but not a Pro, so I'd appreciate any help or suggestions greatly.