Heatdrop triggers Thermal protection

I recently upgraded my Wanhao i3 Plus Mk2 from the stock firmware to the ADVi3++ 4.0.5. At first everything worked perfectly except for some stringing issues and overhang-curling*, but then I had a nozzle-leak and the PLA melted the whole heaterblock into one brick…
After I cleaned everything and reinstalled the parts, suddenly my Printer had a heatdrop the moment when the partcoolingfan kicked in (at layer 2) from 210°C to ~186°C and didn’t recover it’s target temperature before the thermal protection got activated.
My first guess was that I broke the thermistor, so I bought a new screw-in thermistor (I changed the line in the header Configuration.h from 1 to 11). The problem still occured right at the begin of the second layer so I thought the heater-cartridge was damaged. I decided to swap the whole setup to a 6mm 50w cartridge instead of buying a 6.3mm 40w stock one.
After the new heater-block arrived and I put everything together. The first print worked but I still could watch a temperaturedrop from 210°C to ~190°C but it recovered fast enough to not trigger the thermal protection. This time I had forgotten to finetune the PID-Settings, so I did the automatic PID-tuning after the first print, because of the new hardware-setup.
Then on my next prints I got the same result as before: First layer prints good, at the second layer when the partcoolingfan turns on, temperature drops under 190°C and when it starts to recover, the thermal protection stops the printer at ~206°C.
I don’t know what to do next? Maybe I am not seeing the obvious solution? I don’t even know if it is a hardware- or a software-problem, because I think my last firmware didn’t have activated the thermal runaway-protection which could therefore not have been activated in case of a heat-drop.
Please help me!

*P.S.: I got a Diii-part-cooling-fanshroud with a radial fan which I lowered with some washers to fix the overnang-curling problem with overhangs not being cooled fast enough and therefore curling upwards which resulted in the extruder crashing into the part and ripping it off the printbed. Maybe this setup is the problem, but shouldn’t there be a software solution to prevent the quick heat-drop?

I’m sorta having the same issue too, I’ve just ran the CelanEEPROM hex file to see if it helps (reflashed obviously).
mine’s been on the bed though.

I’m re-calibrating the PIDs right now and will test it out and see how things go.

PS @Florin_Gum, make sure you re-calibrate your PIDs after installing the Dii Cooler, it will change the thermal characteristics of the PID on the Hotend.

So I think I have found a workaround by simply reducing fanspeed on the second layer to 50%, the third lever 70% and finally at the fourth layer the fan reaches 100% speed. This way the thermal protection isn’t triggered because the heatdrop isn’t as big as before.
Anyway I hope that I can find a better solution, because with this method the actual problem isn’t gone (especially when I’m trying to change temperatures midprint) but at least I can finally print again!
I re-calibrated the PID settings several times already but - even if I don’t change anything at the position the print head is in - there are every time different PID values.
And when I tune the PID a second time right after the first run finished, thermal protection is also triggered…

The part cooling fan is supposed to blow cool air on to the part to help it cool down faster after it has been extruded.
It you have had an issue with a very large blob, make sure the fan duct doesn’t have something deflecting the cool air at the heater block.

If this jet of cool air hits the block it will drop the temp of the heater block, potentially tripping the thermal protection (do not disable this feature, its one of the best safety features you have)
Second it puts more load on the heater making it work harder and draw much more power, this in turn put more load on the power supply.
It also makes it harder to print with higher temp materials.