In general - OBS can't cause this problem.
Often, folks are unaware of how computationally demanding real-time video encoding is, and don't realize they are overloading their OBS computer, which then gets unstable. OBS isn't the issue... overloading the computer is the problem.
So you should be monitoring your computer to max sure you aren't resource constrained (CPU, GPU, RAM, Disk or Network I/O)
Then, realize that upload bandwidth numbers (from speedtests) are often highly optimistic, and do NOT represent the sustained, low jitter, bandwidth amount, hence the strong recommendation to not set your bitrate too close to your expected upload limit (leave some room for normal ebb and flow)
And then there are ISPs that can't/don't sustain that bandwidth (ie, there may be no issue at your house, or your connection at all). whether that applies in this circumstance depends on your specific ISP (Fastweb in this case)
One thing I've seen is people using either streamelements plugin or other browser based sources, not realizing how poorly written they are and the CPU is driven to 100% (or causes CPU thread locking) and that then causes havoc. This is NOT an OBS issue.
so for basic troubleshooting, I'd recommend a clean scene collection with no plugins active/running, and try a test stream. If that is stable, then you know (during that time at least, your computer, OBS, and your network are fine). And that should help you narrow down the source of the problem. If you still have problems, I'd start with making sure your OS and PC are up to the task (not an old, low-end CPU trying to do high resolution and frame rate, with filters, etc), that the OS is clean with unnecessary processes stopped/disabled (if resource contention is an issue).
With an RTX 3070, why aren't you using NVENC? [oh, later I see you did try it]
17:58:41.226: Output 'adv_stream': Number of lagged frames due to rendering lag/stalls: 115 (0.7%)
17:58:41.226: Output 'adv_stream': Number of dropped frames due to insufficient bandwidth/connection stalls: 743 (4.6%)
then later
18:00:02.258: Output 'adv_stream': Number of lagged frames due to rendering lag/stalls: 46 (3.0%)
18:00:02.258: Output 'adv_stream': Number of dropped frames due to insufficient bandwidth/connection stalls: 737 (50.0%)
Means you need to adjust your encoding settings
and you have a network problem of sending more data than your network allows (where in the network path the bottleneck is can't be determined by the OBS log). Is ANYTHING else (including your game) using upstream bandwidth (which includes TCP reply packets)?
