In my experience, stay away from consumer routers and a lot of these sorts of issues go away. Even something as simple and inexpensive as Ubiquiti is miles ahead of anything in the consumer space. I haven't had a router issue in years. And I use VPN every day.

I don't think age is factor here, routers shouldn't "crash" just because you push some bits through it, 5 years old or not.

Except, what’s crazy is that they do. I have an ISP-provided Xyzel C1100 modem, and sometimes it does just randomly crash and take about a minute to reload if we’re doing to much. I’d buy a good DSL modem, but it happens just under the threshold where I’d buy a $100 modem to fix it.

They are often not actively cooled and not build for high CPU usage and the heat that generates.

Except they do.

And I have no idea why either, just like you said, passing bit around.

I use OP's router (https://www.gl-inet.com/products/gl-mt1300/) and it supports Wireguard out of the box and so far it worked very well (used it for 2 months).

Linksys LRT224 has been great for me, I run a permanent VPN to my aws resources.