1-3s is anyway way too low. Even the watching for changes feature has a 10s delay by default. Deletions will even take 1min. So I guess that’s just what you are seeing, just wait for that amount of time and it will sync. If not, I’d try to find out why it doesn’t work, or if not, then set the scan interval to something like 1min, which is the default without watching for changes.
Why do you want immediate syncing? If this is a multi user environment and you want to about conflicts maybe software that is designed to be used in real time might be more suitable? I love syncthing but it’s not great for doing things simultaneously on different devices