Constraint error on byEventId during sync

Error in status bar:
```
Sync failed because of Error: wrapped DOMException: (name: ConstraintError) (code: ConstraintError) Unable to add key to index 'byEventId': at least one key does not satisfy the uniqueness requirements.
```
In console:
```
Uncaught (in promise) Error: add on undefined failed: (name: ConstraintError) (code: ConstraintError) Unable to add key to index 'byEventId': at least one key does not satisfy the uniqueness requirements.
at Store.add (brawl.js:3685)
8brawl.js:3685 Uncaught (in promise) Error: add on undefined failed: (name: AbortError) (code: AbortError) The transaction was aborted, so the request cannot be fulfilled.
at Store.add (brawl.js:3685)
brawl.js:3676 Uncaught (in promise) Error: put on undefined failed: (name: AbortError) (code: AbortError) The transaction was aborted, so the request cannot be fulfilled.
at Store.put (brawl.js:3676)
brawl.js:686 unable to commit sync tranaction
_syncRequest @ brawl.js:686
```