Welcome to the Community and thanks for posting this issue. I’ve just tried to reproduce this behavior on djay Pro AI for Mac, but haven’t been able to. You should be able to edit the BPM value for any song in djay.
So we can take a closer look, could you please get a video of the issue occurring and drop it here? Just let me know when you’ve done so, and then I can further troubleshoot this with you.
I’m glad to hear things are working as expected now. Just let us know if you run across the problem again.
The Apply button is enabled when you’d like to approximate the correct BPM by using the Tap button in the BPM editing panel. While the track is playing, you can click the Tap button in time with the beat, then select Apply to use this approximated BPM value for the song.