The only other thing I can think of is maybe it is a routing issue in regards to lost packets somewhere along the lines from your end to the twitch server you are using to broadcast.
In saying that, it does not explain why you would have no issue with OBS Classic yet have the issue with OBS Studio, which points to a network configuration issue at your end, or a conflicting program (Most likely an AV program intercepting the data packets to screen it, causing a delay when it bursts the transmission data post-analysis)
Can you take a snippet/screenshot of your network config settings for more info to try & work out if it is a setting issue that is conflicting with OBS Studio, perhaps a dev can chime in as well with more insight?