Fatal error regarding duplicate IDs

[FrittenKeeZ]

Describe the bug
Somehow the content of stache::duplicates had one or more entries without :: so the explode() only had one entry and died on trying to get offset 1.
The problem was resolved by clearing cache.

To Reproduce
No idea when or why it happened.

Expected behavior
The code shouldn't rely on certain offsets existing.

Environment details (please complete the following information):

• Statamic Version: 2.11.3
• PHP Version: 7.2

Additional context
First part of the stack trace:

[2019-01-14 09:17:12] stage.ERROR: ErrorException: Undefined offset: 1 in /app/statamic/core/Stache/Stache.php:384
Stack trace:
#0 /app/statamic/core/Stache/Stache.php(384): Illuminate\Foundation\Bootstrap\HandleExceptions->handleError(8, 'Undefined offse...', '/app/statamic/c...', 384, Array)
#1 [internal function]: Statamic\Stache\Stache->Statamic\Stache\{closure}(Array, '15d4b7bc-2d2a-4...')