That’s most often a WiFi issue. The 
doesn’t require fast WiFi, but it does require strong WiFi.
You stated you reset your router - did you turn everything off and turn them on fully one at a time starting from the wall and ending with the ? If no, try that first.
If that doesn’t help go through the setup.glowforge.com again but this time use a hotspot from your phone (if that’s available).
Make sure your ISP hasn’t “helpfully” updated your service to a 5Ghz line (the requires the 2.4Ghz).
If it’s not WiFi it may end up being a failing cable, which a staff member can help you with, but before that there are a bunch more things you can try!