C# why does computation time increments over time of my node

I have a simple C# node that gives me the location of referenced image as full path.
strangely though, when I first run it it has almost no computation time, but over time it get slower and cloging my computer. After a recompute it is ok again. So something can definitely be improved

load relative file.gh (5.1 KB)
Screenshot 2024-07-22 175854