I have exactly the same problem with Android 8.0 connecting Cisco ISR 4000, IOS XE version 16.6 while Windows 10 and iPhone/iPad IOS 11.0.2 work perfectly. I managed to find an old Android 4.1 for testing the connection. No luck either. Seems Android phones don't fit Cisco routers L2TP/IPSec tunnel at all.
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