The app always syncs at least every couple of minutes, so you should never need to force sync.
It is possible that you making an edit just changed the order of sync. Often, it may not seem like much is happening, but there is actually data updates happening in other projects. So the sync may be going on, even if it doesn’t look like it.
Re: conflicts, Agenda is actually pretty good in this area. We made a big effort to make sure that concurrent changes would merge in a good way.
In short, I think you are just seeing a case of slow sync, or a case where it is doing a long cleanup or something. A force sync button would do nothing, because the app literally syncs every two minutes anyway. I recommend just using the app normally. You should find that it works fine if given a little bit of time to upload and download changes. (Eg if you were offline, and never took your device online, the data can never make it to any other device. Hopefully that is clear. Sync is an upload + download process.)