What are common reasons that would cause a background task to timeout?

I am running a task using pagination and streamining to loop over 166,000 records and modify a field. The task is timing out after around 4 hours and then continues to run consume DB resources for some period of time. I am making 0 external API calls so I cant guess what I'm timing out.

Is the total time a task can run dependent upon the plan a user has? Is there some memory being consumed/eaten up by error logs that is causing my timeout perhaps?

Has anyone else experienced these odd task timeouts?