GS110EMX: 10G ports throttle uploads to 250-300 Mbps

I have the MX version of the GS switch in my network A few years ago I found an issue with an Apple TV causing problems when how i had the MS switch connected to my XS 10Gb switch. Seems to be similar situation here. Once I changed the uplink between the host router, XS505M and GS switch, everything has been working as expected and speed between the GS and XS switches remains at 10Gb and have see no drastic drops in speed. 

Host router 2.5Gb port > XS505M Ethernet port > XS505M SFP to ethernet 10Gb port > GS110MX 10Gb Ethernet port <>GS110MX 1Gb>< ATV works

Similar seen in the IG for the MX switch I have: 

https://www.downloads.netgear.com/files/GDC/GS110MX/GS110MX_IG_EN.pdf

Though mines connected with it's 10Gb port to the SFP port on the XS switch. 

The EMX doesn't really show how it's 10Gb is used in it's IG:

https://www.downloads.netgear.com/files/GDC/GS110EMX/GS110EMX_IG_EN.pdf

I see from the EMX spec sheet there are some differences:

Pre-Defined Rate Limiting Rates: 1/5/10/50/100/500 Mbit/s

https://www.downloads.netgear.com/files/GDC/GS110EMX/GS110EMX_GS110MX_DS.pdf

Not sure how impactful this could be with the EMX. 

The support site for the EMX and MX switches both say "GS110EMX - 8-Port Gigabit Ethernet Plus Switch with 2 Port 10G/Multi-Gig Uplinks" 

So you may need to configure the switch for it's designed intended use for the 10Gb port. These seems to have this particular configuration requirement here.

Has a reset been performed on it and setup from scratch? 

Be sure to use good quality LAN cable. CAT6A STP is recommended for connections 2.5Gb or higher.