I'm having this problem too, synch-ing about 300Gb of data in a big folder.
Basically the sync never finishes and the whole Synology server crawls (I have 1Gb in it but I can't add more as it an un-upgradable version), with web based access taking 10 minutes at a time to get anything to run and the hard disk is constantly thrashing/swapping.
Could Resilio Sync be doing ridiculously large re-allocations as it indexes and on a system with limited memory and quite slow swapping to disk (plus slow memory in the first place because of memory compression in Synology's OS) and this just causing everything to crash to a halt?