I have a layman understanding of the pricing structure so it's probably not entirely true "paying the highest spot price in the EU" directly but given I was paying 5-10x more for electricity in December 2022 than ever before my best guess is that when Germany was paying a lot more for electricity due to an increase in the price of gas-generated electricity we were affected by the dominoes falling: electricity would be sold for a higher bid if exported to Germany (or to a zone neighbouring Germany which would be selling to Germany) which caused a shortfall in my zone (SE3) increasing the bid price.

So even if it was a second order effect I had to pay much more than ever before due to increased spot prices in other zones.