After many hours of debugging, I believe I have found a solution to the memory leak problem. Unfortunately, its going to require me to refactor a decent chunk of the scripts. So it may be a couple more days until I am able to upload the new version.
Viewing post in GMS2: Grid-Based Pathfinding Scripts comments
I have just uploaded version 1.1 of the scripts and reference project! To my knowledge, all the memory leak bugs have been fixed. In a test project, I called all three algorithms every step for 5 minutes straight and saw no increase in memory usage. So hopefully this will solve your problem.
I apologize for any delay this might have caused in your development. As always, if you have any more issues with the scripts, you can post again here or message me on Twitter.