Huge amount of crashes when people update my app

[max-de-bons-plans]

At each update, since I inserted Firebase, Google Dev Console shows a huge amount of crashes like this

java.lang.RuntimeException:
at android.app.ActivityThread.handleCreateService (ActivityThread.java:3529)
at android.app.ActivityThread.-wrap4 (Unknown Source)
at android.app.ActivityThread$H.handleMessage (ActivityThread.java:1786)
at android.os.Handler.dispatchMessage (Handler.java:105)
at android.os.Looper.loop (Looper.java:164)
at android.app.ActivityThread.main (ActivityThread.java:6944)
at java.lang.reflect.Method.invoke (Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run (Zygote.java:327)
at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1374)
Caused by: java.lang.ClassNotFoundException:
at dalvik.system.BaseDexClassLoader.findClass (BaseDexClassLoader.java:93)
at java.lang.ClassLoader.loadClass (ClassLoader.java:379)
at java.lang.ClassLoader.loadClass (ClassLoader.java:312)
at android.app.ActivityThread.handleCreateService (ActivityThread.java:3526)