Personally, I would recommend using the external Mosquitto server at this time. I’d give the embedded broker a bit of time to mature a bit before I’d rely on it.
I’d also stay away from the snapshot builds unless you want to help find and solve the many many problems that have popped up with the merge of ESH back into the OH core. Though I don’t think any of those changes should be a cause of the problem you are seeing.
It does sound like you may have discovered a bug in the embedded broker. Please file an issue on the openhab2-addons repo. See How to file an Issue for details if you need help.