I'm experiencing (suffering) something similar, an encrypted folder is synced unencrypted to 3 hosts and encrypted to 5 more hosts.
The 3 unencrypted can sync the whole set of folders and files ( ~ 158Gb), the other 5, at some point fail and stop to sync with similar messages:
EU4FYUQHKNAO4MJGYCPYKSN3SVLIT73XRYQBYYY/OPVPZWOW5C6NQBRICAHUDSGD54/3KDQ4FMA5RYFMMJWLE4RDOUBVA/X4AHX4NRBNSLI5SWGQ7KCHEXOE/JQOOQTUW42VVYEIKCWA2UHORAXE7PIT2U4J4ZTBBX7MCLFMTYVGYDWR5IH636UF5ANYSTD57KA23O/2D2IYQ2DOUNBBZOCWXIOYNKQL4]: state:SEED error: meta:1 conns:1 io:0
[20170109 06:54:00.802] PC[0x00007f0d682a38e0][0x00007f0d607ecf80][188.8.131.52:59999:TUNNELL] disconnect - reason: "Is seed", wb: 0, error: 0, ref: 0
[20170109 06:54:00.909] JOURNAL: Mutex file check failed with error : 103
[20170109 06:54:01.170] JOURNAL: Mutex file check failed with error : 103
[20170109 06:54:01.170] JOURNAL[4AB2]: Mutex file check failed with error : 100
with version 2.4.4 on all ends (some 32 bits, others 64) and a qnap running arm version of binary.
I was able to start syncing from '0' on an encrypted peer (empty folder) until some point where it just stops and one of the curious things is that different hosts show different number of missing files to do a full sync.
Have you figured out what's going on?