So I recently built a PC for editing and gaming use and it's pretty beefy. Here are the specs: Ryzen 9 3900x, Nvidia 2070 Super FE, and 64GB of Corsair Vengeance Ram. HOWEVER, whenever I finish editing within Premiere and try to export I run into a rather strange issue. I use the hardware encoding feature available with my GPU and, for some reason, the estimated export times are ludicrous. For example, I just made a very simply edited video but rather lengthy (about 16 minutes). The estimated export time said 4 hours and 46 minutes and showed no signs of progress when I left it alone. I then moved my project over to my MacBook Pro which is also rather beefy (2.9 GHz i9, 32GB Ram). When exporting the same project, this time with software encoding since the hardware encoding is not available on MBPs, the export time estimated at 16 minutes. At this point, I moved the project back over to my PC and tried encoding AGAIN using hardware encoding and it took 8 minutes. I'm extremely confused about this issue and haven't found any post pertaining to it. If this helps, I edit off of an external G-Drive 4TB.
Lots of things can mess with render times. Maybe your computer was busy doing something else, maybe the hard drive was busy doing something else. Depending on the effects you apply it can take longer etc. Without a bit more detail, it's hard to pin down exactly what would cause such a change but likely it's just the computer was bogged down with some other process?
Definitely an issue with the versions. I was having the same issues. I never ran into the issue (even with multiple software running in the background) til I update to 14.5. So I rolled back to Premiere Pro version 14.3.2 and my export speeds are way faster now, 12 mins to export a 40 min video. With the latest update, I was exporting the same video at 1 hour for a 40 min video.