Thanks for reaching out. We didn't do a firmware upgrade, we'll be sure to put out a notice if we do. There may be a configuration oddity or bandwidth throttling happening when it shouldn't? However, that doesn't sound likely (it seems you haven't made any changes).
When it comes to wireless suddenly changing speeds, it is almost always channel selection and utilization. In fact, it jumps out to me that the ASUS AP and GR10 are most certainly on separate channels. Finally, the GR can automatically change channels. While it tends to do this to make improvements, perhaps it made it worse. Have you tried checking out the wireless channels in use? I'd check the following:
Plug in that ASUS AP, see what channels it is using and what bandwidth if possible (20, 40, or 80 Mhz).
Plug in the GR10 and do the same, find out what channels it is broadcasting on. You can do this in the app and even select which channels to use (Hardware > GR10 > Radio Controls in the app).
When connecting a laptop, check which band it uses on both the ASUS and the GR10. This could be either 2.4 Ghz or 5 Ghz bands.
2.4 Ghz or 5 Ghz can both work well, it just depends on how "busy" the channel selected is.
Your neighbor may have even installed an access point that was conflicting with the GR10 channel but not the ASUS.