I'm using the Unreal Crash Reporter Client to send events, but many of my events are showing as invalid and does not appear in my issue stream.

Sentry requires log files sent with the crash to be serialized in UTF-8. If they are not, they will show as Invalid on your Stats page, and dropped by Sentry server side. The events are not recoverable.

Note: There are other reasons why an Unreal event can encounter processing errors on Ingest leading to "Invalid". This is just one of the most common reasons.