Where did the upload speed go?

[#1]

Two things happened this week. I disconnected, reconnected to pick up my new static IP address (thanks Plusnet, what happened to the second email to tell me when you changed it) and I was doing some work yesterday which required that I switch off the power in the house and thus, had to power down the modem.
Now I didn't test in between these two events, so I don't know which is it, but since these events, my upload speed has collapsed from 17Mbs to 1Mbs. Any one had any experience of this? I suspect that it is the power down, but I did the same a few months ago with no ill effect, so what is going on?
What is the best way to recover, a reboot, or leave it alone and cross fingers?
Phil

[#2]

Hi Phil,
I've just tested your line and the results are saying that your upload is still in sync at 20Mbps, so there's nothing obviously wrong that I can see from here. If you continue to see poor throughput it may be worth opening a fault for us to investigate further.
Downstream Speed 80.0 Mbps
Upstream Speed 20.0 Mbps
Profile Name 0.128M-80M Downstream, Error Protection Off - 0.128M-20M Upstream, Error Protection Off

[#3]

Chris
Thanks for the quick response. I'll get on and raise a fault. Downstream is fine, just upstream.
Phil

[#4]

Chris
Just went to raise a question, but got into a live chat instead. Chat agent checked profiles etc all seems to be OK. Finally got to do a BT speediest, I've been getting Http 500 server errors all morning, all confirm profile is correct.
Chat agent suggested connecting direct to modem using PPoE to test there. Did the connection, upload speed is fine again. So, I'm thinking a router problem. However, I connect the Mac back to the router again, run the speedtest and the upload speed is also fine there.
All I've really done, is set up a new connection, run speed test, disconnect the new connection and plug back into router, bear in mind the router hasn't been rebooted or anything and the speed is back to normal. Even more confused now, happy, but confused.
Phil