If you didn't update the app, then something else might have been updated. System webview was updated in January 30th, did the crash rate changed after that date?
It seems like it started to rise before that, but I think maybe I should try using crosswalk webview plugin and see what happens.
I've recently seen a spike in Android crashes too, specifically in the new Android 8.0. For me, it was related to the camera plugin which needed updating for compatibility.
Take a look at HockeyApp;
<plugin source="npm" name="cordova-plugin-hockeyapp"/>
This catches and reports crashes back, allowing you to see the stack trace, device info and any app specific meta data. As PGB does not export the debug symbols, it is not always clear but gives you a good idea to what is going on, where and what devices / versions.