As an IT person, not someone super knowledgeable on OBS Studio and Streaming protocols, using dynamic bitrate is a workaround to an unstable network connection. Best solution - fix your network. The problem is, that isn't always easy, practical, or within the OBS Studio user's control.
LOTS (innumerable) threads on this issue... start with not using wireless technology (no WiFi, not cellular ISP, etc). Then, be aware of overall LAN traffic - is there other LAN (for OBS Studio PC or other devices) upload/upstream data traffic that is causing a conflict? FYI - there is NOTHING in OBS Studio log that will really help... this is network troubleshooting 101, and has nothing to do with OBS Studio. As for why OBS Studio streaming is the only app impacted, and all else on LAN seems ok? When that happens, usually because there is no other unbuffered outbound traffic that is Latency and Jitter sensitive like livestreaming. Web conferencing comes close, but usually uses patented traffic shaping algorithms to work around WAN link instability. Such is possible for livestreaming, but NOT on any of the free consumer services, that I'm aware of. Other than things like OBS Studio's dynamic bitrate, which is again, a workaround, not a fix.
When you drop the bitrate and it appears to work, then you've found the threshold of consistently available bandwidth at that moment. Other traffic can change that threshold ... it is usually NOT a fixed, always true #. And some setups (WiFi, etc) are FAR more variable than others. But just as freeway traffic can vary, so does Internet traffic, and 'traffic jams' can occur, sometimes completely out of your control