WS2813B RGBW help needed

Hi

I did the remote control for a large LED setup and was asked to also have a look at the sometimes non
working LED strips.
There are 5 strips of 67 WS2813B rgbw leds connected in series, a total of 335 leds.
Problem is, that every once in a while one of these strips only switches off every second led, the leds in between stay at their last value.
When the complete strip is switched on again, they also stay at the same last value.
Switch on/off is merely the data signal, power stays on.
Some of these single strips go completely haywire, although input signal is good.
Strangely it worked last winter for 3 month without flaws.
When asking the supplier for spare strips, they told me, these led chips aren’t made anymore, because of stability issues.

I there anyone out there with the same experience with these chips ?

I’checked :
Voltage supply in spec : 4,4V to 5.1 V, no spikes.
Signal in between strips is nice and square.
Timing is a bit off from the spec around 600ns for T1L this is a bit longer.than recommended But these are the signals produced by the led chip itself
all connectors and soldering, no corrosion.

Looking forward to any answer and thanks

Harald