@HCP so after have been verifying 2 or 3 times, I finally added the fees and the total match the balance showed in BRD slow sync or eletcrum.
Crazy that the fees made such a huge difference to the balance! That's quite a substantial amount spent! :O
I am gonna continue to better understand what was these 3 transactions that don't appear in Fast Sync. Do you have any the idea why these 3 transactions didn't appear at first ?
The only reasons I could see for them no appearing in the fast sync would be some sort of "Gap Limit" limitation (ie the system was simply not generating enough "new" addresses to check and missed those 3 transactions) or it was caused by some sort of timeout in the sync process.
I'm not overly familiar with BRD as I haven't used it in years (As I recall the app wouldn't run on rooted devices and I was heavily involved in Android Custom ROM development at the time so was using rooted devices) so you would need to talk to the app Dev(s) and ask them why the fast sync misses those transactions... fastsync is some custom system they have developed to replace SPV, so it might be a bug that they can fix.