Audacity randomly slowed down

I’m running Audacity on Windows 10 and have been doing so for quite a while to produce a weekly radio show. The show is roughly an hour long and all I need to do is run it through a compressor. For my first 2 dozen or so times doing this, it works fine, despite the hour long file. It takes a few minutes (2-4 or so) to compress the whole thing. Today I tried to do it to another episode at its taking well over an hour. Nothing about my PC, OS or audacity has changed. Why might this be happening? A restart of the comp changed nothing.

What is taking over an hour?