Ubiquiti Dream Router Throughput Issue

I've been a proud owner of a Ubiquiti Dream Router for a good while now - live in a rural area so the Dream Machine would've been overkill for my needs.

Currently getting 300/300 from the ISP. Not bad.

Couple months ago, noticed I was getting some pretty awful speeds to my end devices, around 30/30 across the board. Wired/wireless made no difference.

Checked the periodic speed tests the UDR does, nothing; no change in bandwidth.

I hadn't changed a setting in my router in quite a while as I've been happy with my setup, so I was convinced it was a fluke. Rebooted, back to semi-normal speeds (though still short).

After dealing with this for a while, tonight I finally decided to bite the bullet and factory reset the UDR. Throughput right back to normal immediately. Restored backup - throughput still where it should be.

Am I missing something obvious??

Edit - to clarify, when I checked the speeds from router to isp, I'd been getting expected bandwidth the whole time; it was only the end devices suffering.