I recently purchased a Deco M4 3 pack and everything has been working great. Running RL. 45372. I quickly realized that I would need more ethernet ports for home office. We have 3 computers and the deco leaves me with 1 ethernet port. I purchased a TP-Link 5 Port Gigabit Ethernet Switch (TL-SG105) to expand the number of ethernet ports available to me. 

However, I immediately noticed an issue. Running 3 different speed tests my download speed went from 250mbps to 10 mbps. Upload was unaffected and as expected. I then removed the switch and plugged primary desktop into the deco and my download speeds were back to normal. Is this not a viable setup for the deco? I researched the switch and it shouldn't be the bottleneck, but it appears it might be.

Any suggestions as to where I should start? Did I buy the wrong switch or is there a setting I'm missing? Or is the deco m4 not compatible for the switch?