Do you see events rate limited in the Stats page? Like:
There are different places that data can be dropped. The SDK could be dropping if the transport isn’t fast enough to flush them out. The Java transport has a queue of 30 items but not long ago was only 10.
Version 3.1.3 moved to 30 so you should be fine.
What’s the max throughput in requests per second do you have on this server? Could be that some bursts are caught up in this backpressure mechanism and end up dropped. You could try making this queue larger through setMaxQueueSize.
When the event makes into Sentry, it could be dropped due to spike protection which is there to help you save your quota. Or some other filters like inbound filters.
The SDK has a debug mode but if this is a high throughput server you’d need to add a customer logger to it and dump somewhere as obviously looking at the console wouldn’t help.