Reported on the mailinglist:

Running my app using JNA 5.3.0 on OS versions prior to Android 8.0 (API level 26) results in the following stack trace:

--------- beginning of crash

04-24 17:02:35.617 12484-12484/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.bugsbegone.myapp, PID: 12484
java.lang.NoClassDefFoundError: Failed resolution of: Ljava/lang/invoke/MethodType;
at com.sun.jna.internal.ReflectionUtils.(ReflectionUtils.java:77)
at com.sun.jna.internal.ReflectionUtils.isDefault(ReflectionUtils.java:135)
at com.sun.jna.Library$Handler.invoke(Library.java:231)
at java.lang.reflect.Proxy.invoke(Proxy.java:393)
at com.bugsbegone.myapp.$Proxy2.mylib_init(Unknown Source)
[... My app specific trace ...]
at android.app.Activity.performCreate(Activity.java:6270)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2382)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2493)
at android.app.ActivityThread.access$1000(ActivityThread.java:150)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1357)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5446)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:743)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:633)
Caused by: java.lang.ClassNotFoundException: Didn't find class "java.lang.invoke.MethodType" on path:
DexPathList[[zip file "/data/app/com.bugsbegone.myapp-1/base.apk",
zip file "/data/app/com.bugsbegone.myapp-1/split_lib_dependencies_apk.apk",
zip file "/data/app/com.bugsbegone.myapp-1/split_lib_slice_0_apk.apk",
[... lots of slices ...]
zip file "/data/app/com.bugsbegone.myapp-1/split_lib_slice_9_apk.apk"],
nativeLibraryDirectories=[/data/app/com.bugsbegone.myapp-1/lib/x86_64,
/data/app/com.bugsbegone.myapp-1/base.apk!/lib/x86_64,
/data/app/com.bugsbegone.myapp-1/split_lib_dependencies_apk.apk!/lib/x86_64,
/data/app/com.bugsbegone.myapp-1/split_lib_slice_0_apk.apk!/lib/x86_64,
[... lots of slices ...]
/data/app/com.bugsbegone.myapp-1/split_lib_slice_9_apk.apk!/lib/x86_64,
/vendor/lib64, /system/lib64]]
at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
at java.lang.ClassLoader.loadClass(ClassLoader.java:469)
at com.sun.jna.internal.ReflectionUtils.(ReflectionUtils.java:77)
at com.sun.jna.internal.ReflectionUtils.isDefault(ReflectionUtils.java:135)
at com.sun.jna.Library$Handler.invoke(Library.java:231)
at java.lang.reflect.Proxy.invoke(Proxy.java:393)
at com.bugsbegone.myapp.$Proxy2.mylib_init(Unknown Source)
[... My app specific trace ...]
at android.app.Activity.performCreate(Activity.java:6270)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2382)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2493)
at android.app.ActivityThread.access$1000(ActivityThread.java:150)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1357)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5446)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:743)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:633)
Suppressed: java.lang.ClassNotFoundException: java.lang.invoke.MethodType
at java.lang.Class.classForName(Native Method)
at java.lang.BootClassLoader.findClass(ClassLoader.java:781)
at java.lang.BootClassLoader.loadClass(ClassLoader.java:841)
at java.lang.ClassLoader.loadClass(ClassLoader.java:504)
... 21 more
Caused by: java.lang.NoClassDefFoundError: Class not found using the boot class loader; no stack trace available

The breaking change is [GITHUB-813] Support binding interfaces containing default methods, which resolves #813.
Unfortunately, the MethodType class doesn't exist in Android until API level 26 (https://developer.android.com/reference/java/lang/invoke/MethodType).

It would be a shame to have to undo this new feature for backwards compatibility, but it does wipe out JNA support on >75% of current android devices.
Maybe a separate branch for Android would be the best way to allow bug fixes etc. to continue, but without any of the unsupported Java7+ features?