Hello I think I have the same problem.
Between 3 NAS: DS411+II (x86) , DS1515 (Alpine) et DS211+ (88f628x) . using the last version 2.6.2
I synchronised movies and a lot of files waren't synchronised. There were data transmission between clients, creation of the temp file "xxx.!sync" in the .sync folder. But After i have in the history tab of the sending client "failed to download FILENAME readfromdisk " nothing in the receiver client and nothing else happened.
It was when it was the DS1515 the sending client. No test with the others.
I don't had the idea to check a 2 Gb size limitation, but I remember that some files under 2Gb synchronised well.
I will check that, when I will have time, perhaps this evenig (Resilio is off today, I use one direction synchronisation with Synology internal tool in backup solution. )
Perhaps the bug has a link with this power settings? I don't try to change it.
torrent_max_piece_size
int
2097152
in bytes. Decrease piece size to reduce delta diff when syncing. Downside might be reduced speed and higher CPU usage