Query takes 17 seconds, export grid rows takes forever

Hello,

I run a query that takes about 17 seconds to complete. However, to right click the results and choose 'export grid rows' takes probably 5-10 minutes just for the save dialogue to show up, then another 50 minutes to actually save the output.

Take a look at the attached image to see the query (can't copy&paste now as the dialogue is in state (Not responding)

Why is this so slow? Are there some settings I can adjust?

I am using HeidiSQL Portable 9.5.0.5196 (and had this problem with all previous releases also)