So I've got a ws2815 strip with 300 LEDs, and can't get it to work with GPIO 18 on RPi 3B+. I've tried it both with and without level-shifter. Not only Hyperion doesn't make the strip light up, but also other software like Adafruit Neopixel library. Best I could get via Neopixel is either all-white or random colors. I tried various settings (freq 400 and 800 kHz, DMA channel 5 and 10). It feels like the problem is on software side, but I don't know what else to try, as others have reported this chip working with rpi281x library just fine.
At the same time, the strip works perfectly fine with the stock SP107E controller. So at least I know it's alive. I've also measured the output levels on the Pi, and level-shifting seems to work correctly.
Thanks a lot for any help!