Some users are experiencing crashes in Play Music v7.9.4920 according to reports from users who have recently updated to this version of the application. What's more is that the crashes are said to be happening immediately upon opening up the app, so the crash seems to be a direct result of the update, though it is worth mentioning again that this isn't happening to all users who have the latest version of Play Music.
Based on the reports the problem doesn't seem to be stemming from the software version of the operating system that devices are running on nor does it seem to be a problem that is specifically happening for a particular type of device, as a wide mix of different devices and Android versions are all experiencing the issue, including Pixel devices, Galaxy S7 devices, Nexus 5X devices, and with both Android Nougat and some versions of the Android O developer preview. While it hasn't been confirmed yet, it's possible that the bug that's causing the crash has to do with Bluetooth audio being on and trying to connect before opening Play Music, as some users look to be reporting that disabling Bluetooth first, then starting Play Music and trying to reconnect to Bluetooth afterward avoids the crash, so that might be worth trying. With what appears to be a larger number of people having this problem it's likely that Google is working as quickly as possible to get a fix out seeing as Play Music is one of its bigger and more popular applications and services, but at the moment it doesn't look like there is an explanation from Google on the issue or a time frame for the fix to come through.
For those that are experiencing the issue the workaround it would seem is to try and revert back to the previous version of Play Music if you can, or perhaps use another streaming music service like Spotify if you have it or don't mind using the free version that comes with ads. If you haven't seen the issue yet but you aren't sure whether or not you've updated to this version of Play Music, you may want to double check to see if the app has been updated and if not, avoid it for the time being just to be sure that you don't run into this problem.