I can’t be the only one to have this problem.
Some Networks are fast. Some are slow.
If I speed limit all of syncthing, that slows up big LAN transfers. If I allow network traversal while on a slow network, that saturates the network to a crawl. I can’t win.
For now, what I have done is to disable NAT traversal on my home server.
I am thinking of using another sync solution just for very small files. If you are looking for a solution, I hope this helps.
However, maybe you have a better solution, such as a way to get syncthing to remember what to do on different networks?