Sluggish NAS Performance with AFP

Question

Just got my self a NAS (Asustor AS1002T) to handle my files. It is supposed to be up to 110MB/s read and 90MB/s write, it has two Seagate 2TB Barracuda running in RAID 1.

The Setup

I have a Archer C7 router connected to my ISP modem (internet in port), and then the NAS connected to the Archer C7, which has a gigabit connection. I access the server via WiFi with my iMac running High Sierra. All wired connections are Cat5e.

The problem

Sluggish performance. It takes more than 1 minute for a 100 MB transfer. More than transfer times, Finder is really slow showing files - in a tree-like structure, it takes a few moments to load the contents inside the tree. Deleting a 10kb Python file from the NAS takes about 10-15 seconds, and it looks like it does not understand the process in question (does not say how many files are being deleted, nor the estimated time remaining).

Navigating with the File Explorer of the NAS, running within the web browser is a lot faster than navigating with Finder. When using a wired connection transfer times seems fine, but I still get that slugginess when navigating with Finder. Inserting data to a NAS-hosted DataBase (MySQL) is ridiculously slow (15 inserts/second), simple SELECT queries take about 5 seconds to run.

Blackmagic Disk Test says wired connections are running at 60MB/s write and 100MB/s read, and wireless connections are running at 45MB/s for both write and read speeds, but it sure doesn't feel that way when working with the unit.

Ping seems ok: no loss packages, with 1.4 ms avg time. My internet connection seems ok: still getting the speed delivered by my ISP provider with no problems.

I'm running AFP, with everything disabled (SMB, FTP, WebDAV, etc). Any ideas what can I do to troubleshoot and fix this?

Thanks a lot.