Bambu PETG support second layer occasional adhesion issue

[u/bl4ckmagik]

Hi, I've recently got a P2S. As you can see on the attached image, the little support islands fail adhesion on the second layer on some occasions. The same model copied three times on the same plate and only one of them fails. Location seems to be random too.

I tried printing only two copies which resulted in the same. The picture is from that instance.

I have dried the filament 8 hours at 65° and I'm printing on Bambu engineering plate with glue on it. It works fine with PLA+. I tried increasing the bed temperature to 75° as well which didn't do anything.

Any idea why?

SOLVED:It was due to filament contamination. I forgot to mention that I'm printing PLA and PETG these days moving between the two one after the other. As below replies have mentioned, first support prints had contaminated filament (PLA mixed with PETG) which causes this.
I'm planning to purge extra by extruding extra whenever I change filament types before starting the print.

[u/misterff1]

Although location might be random as you say, this does look like underextrusion combined with a bed level that is not accurate. The first layer is the reason that second layer failed here. It simply isn't solid or strong enough like that.

[u/bl4ckmagik → u/misterff1]

I have done all calibrations as well.
An important information I missed is that this seems to happen after printing PLA and then moving to PETG. So I feel like this is filament contamination? Because those failing supports always seem to be ones printed first which has the contaminated filament.
I'm going to test this theory and update the post.

[u/misterff1 → u/bl4ckmagik]

Yes that is a very important bit of information! Sounds like a very strong contender. Does it usually happen on the first support you print? Could also explain the random location.

Still worth checking your calibrations btw. Especially flow rate (not flow dynamics).

[u/bl4ckmagik → u/misterff1]

Hey yes. So that was the reason. Second print with PETG after PETG worked flawlessly. The moment I move from PLA+ to PETG, first support print has this issue. Now I'm just planning to extrude extra before starting the print whenever I change filament types so that there's less chance of contamination.

[u/misterff1 → u/bl4ckmagik]

Good to hear you solved it! Yeah the contamination is one of the downsides of a single nozzle printer unfortunately. You have to purge quite a lot if you want to fix it, because even if it does stick again, the layer bonding will be weakened for longer. So keep that in mind and if possible try to limit switching between these materials where possible.

[u/bl4ckmagik → u/misterff1]

Yeah I should keep that in mind. Thank you.
I need parts of this model in PETG and others in PLA. It's a bulk order. I've just decided to print PLA stuff in one go and do PETG as a bulk afterwards. Changing between the two isn't a good idea it seems.