K8064 Dimmer flickering with 650W

I assembled the K8064 dimmer and it seems to work. I use a 0-12v input and 230 V with a 650W theatre lamp.
However after a few minutes the low light settings start flickering.It seems to get worse the longer it stays on.
I have searched this forum and checked all suggestions (c12 = 100nF, TRIAC = TIC225M bourns, c13=0,47 uF). Only thing I haven’t tried is replacing the TRIAC. Are there any suggestions/solutions for where this flickering comes from?

Hans (NL)

The trigger current for section IV is by far not sufficient (major design flaw). The TRIAC will only trigger in section I, conducting only DC. This will damage inductive loads. I do not see an easy solution for that, the µC is not able to supply the required trigger current even if R5 is reduced.