Rendering split videos takes forever

Hello everyone,

maybe you can help me with this issue.

I'm a youtuber (Let's Plays), so I usually record ~3 hours of content at a time, and then split the content into different files (~30 minutes long). I record audio commentary seperately, and match both audios up in Premiere Pro.
Since one of the last updates, I noticed that Premiere Pro takes longer for each segment to render.

The first part, minute 0-30, it takes around 20 to 30 minutes to render in 1080p60.
However, each subsequent part takes exponentially longer, up to the point, where the last part (2:30h to 3:00h) takes around 4 to 5 (!) hours to render, as if he needs to render the whole file up to that point and then cut the requested sequence out.

This behaviour did not occur when I re-started Let's Playing back in may, so I assume that during the summer, one of the updates caused this behaviour.

Steps to Reproduce:

1. Import a large, long file (.mp4)
2. render it in subsequent parts, each around 30 minutes long, 
3. observe how with each part, the rendering time increases compared to the previous part

Can you confirm this performance issures somehow? And do you have a workaround for this?

Thank you very much in advance.

Kind Regards

Sascha