I have my default temperature set to 245°/100° for my extruder and printbed respectivley. Even after preheating to those temperatures it lowers them to 205°/65°, and cools too quickly to get the print started. Do I need to change values somewhere other than "Deafault" in printer settings?

I would try reslicing your stl file, that worked for me. ( I believe it then uses your default to change gcode)
Hope this helps.
Rod

Normally you set temperatures in your slicer config. That overrides any temperature setting you did before. Check your filament settings in the slicer.

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