I seem to have issued with shifted layers on my +Ultimaker II extended.
This only started recently after about 30% of that  large failed print last ween and it happens now every time after just a few layers.

The only thing that has changed is that the weather has gotten very, very hot recently.
(We may get the hottest day in Germany in recorded history today.)

* checked that all bolts are fastened
* greased the (very dry) X and Y rods
* having an AC try it's best to reduce the room temperature <30°C.
* checked all grub screws on th pulleys
=> this did NOT help.*
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