Bump. I am interested in a reply to this one.
My gut believes this looks like insufficient detail vs artifacting (difficult to guess from a still though), caused by too much IR reflection.
It just looks like too much IR light at the front bouncing back from the drive and fence, so the camera can not get the correct background exposure.
Is that a streetlight, you may be able to force day mode at night, although you may need a cam with 0.0005 Lux, compared to this which is 0.001 Lux (I think from memory)
Turn Up the IR (Manual) = Over Exposure Up Front (HLC or SSA may help compensate)
External IR = Cost and Visual Impact
Lower Shutter Speed = Motion Blur
I have said this before, but I honestly find the IR on the Dahua's quite poor, compared to the cheaper cams with the ring of smaller LED's around the lens (but they suffer from spiders and webs here in Oz)
There is talk of Firmware tweaks, but at the end of the day Dahua's approach of a single or dual high powered LED just doesn't have the throw distance and cause too much bounce back. Physically with a single LED you can't have one targeting throw in the background and also the front.
Think of a torch you can go for the wide throw and you just don't get the light at the back, you can tighten the beam and get good light in the distance, but you need both for completely coverage.
Try something like this.