Speed has halved

[#1]

I've been on the unlimited fibre 38/1.9 package for just over a week, using a TP-Link TD-9980W modem/router and self-install. I was getting speeds of around 36/1.9 initially, which I was delighted with. However, in the last few days the download has reduced to 18-19 Mb.
I've attached screenshots of the speed test and modem status.
Please could someone take a look and let me know what might be wrong?

[#2]

Our testing isn't showing any issues.
Can you try a wired connection?

[#3]

Good call Matthew. Thanks. Wired connection speeds are fine.
Having inspected my wireless setup, I have a clash of channels between the router and a repeater that I have, and suspect this is causing the problem. Will reconfigure.
Sorry for the false alarm.

[#4]

Glad to hear that!
Fingers crossed that's the problem.