Time Machine - backup extremely slow

Hello everyone!

I am looking for help with a making extremely slow backup using Time Machine to My Synology drive by AFP protocol.

The first backup takes several dozen hours (~10h) - OK, sometimes I can understand it - but why he send files at ~ 300 kbps where 100 Mb/s is available ?!

Unfortunately later, differential copies also performs very, very slowly at the same speed about ~300 kb/s

- battery is fully charged and the mac connected to the power supply.

- it is not overheated.

- does not use CPU or disk IO (write/read).

- I do not have any anti-virus or firewall.

Honestly - I did the test at night, where I sleep - mac was working at all night (of course he's not done)

It is not the fault of the network..

- Testing network...

I download a 1GB file from the internet directly on synology drive (using wget by ssh on synology ash shell) - downloads at the speed of ~300 Mb/s ⚠

I tried to mount my share using afp:// on my mac and using the "Finder" I drag and drop the 1GB file to directly mounted share and surprise it sends at full of network - ~90-95 Mb/s

...so where is the problem?!

on strange luck the same effect is on 5 other Mac's (air and pro) - everyone has an updated system.

Please help.