Dropbox upload sync is very slow

I run a small video production studio and we use a Dropbox advanced plan to sync our files to the cloud. For the past couple of years we have had no issues syncing hundreds of gigabytes a day at speeds typically averaging 300-400mbit/s. 

However, over the past few weeks, those speeds have dropped drastically and now we're lucky to see 10-20mbit/s, so our syncs are often taking days to complete.

This is happening on different devices, different networks and even on different home/office internet connections. Our main network is 10 gigabit and we have a high speed 1 gigabit fiber connection.

Given that this is occurring across so many devices on different connections, I can only assume the issue is at Dropbox's end. However I'm not having any luck with their support. 

So I figured I'd try here. Has anyone had a similar issue and been able to resolve it?

TIA.