Making the sftp server and still not know the cause of problem

Solution 1:

The issue here is that you can only have one default gateway and you have two and enp5s0 is defined first, so that takes all traffic and enp6s0 gets none...

That leaves you with the following possibilities:
(all are mutually exclusive, the higher the number, the more difficult)

1. You can have one of the two IPs face the internet (default) and the other one internal only. (static routes)
2. You need to add a 3rd external Internet router (E.G. A Cisco ISR 111x with dual WAN ports) that will bond the 2 external routers you already have and will save state for the external connections and set that router as the default gateway for both (on different IP addresses)
3. You can bond both NICs together and let the bond save state: you have no control over what goes where: the bond does that for you like the third router would do in hardware.
4. You can split up the internet in 2 and define half of all Internet address ranges on #5 (Let's say all of the USA; static routes) and all of the rest of the world on #6 (default).