Print shifts with certain color

[Yeshead]

I printed an object where at some point the whole thing shifted.This has happened to me twice now with the same color but with 2 different objects.These objects were quite large.It is about ultra marine blue PTEG from Prusa.The printer is an MK4SThe nozzle is standard and is at 240° and the bed at 85°The attached photo shows that the whole thing shifted at 2/3 of the print.After the print was finished the whole thing was "fixed" on the bed and therefore not loose.There was a hard bubble on the edge (see green circle) and the arrow indicates how much it shifted.A hard bubble can also be seen on the inside (see green circle)It looks like "something" is burning.I don't have this with other colors.Does anyone have an explanation for this shifting? As mentioned, this is now the 2nd time this has happened (with a different object)