What version of PsychoPy are you using?
I am using v2023.1.3.
Update: I managed to resolve the issue. I re-coded the experiment step-by-step and identified that the incorrect translation was caused by a trickle-down effect, i.e. an arrow-shaped polygon not being translated correctly. I made the necessary corrections (thanks to this post: I need advice about one stimuli - #8 by shabkr), and now everything is initialized as expected.