Last few LEDs not lighting up on start

I have a long strip of ws2814 12v. Discovered that 388 LEDs are fine, but anything beyond that does not light up at start. I have total of 403 LEDs.
I thought it might be broken chip at 389 position, so removed it and soldered back together. That didn’t help, same issue.
I tried connecting the remaining piece of strip to another channel. Channel 2 was configured to start from 389 and be 20 LEDs. None of them light up.
However if I reduce number of LEDs in first segment to say 350, then the second channel starts working. This gives me thinking that strips themselves are fine as they can work individually

Some more experiments I did:
On full strip of 403 LEDs set in settings length of 388. Then change to 389 and it lights up. Keep increasing length in settings by 1-3 and they gradually all light up just fine. At that stage it can work for quite some time, then after few hours reverts back to 388.
Does not seem to be related to power output

Using quinled-quad board. Wled 0.15.0