Chrome can't access router over socks5 proxy anymore

Question

I have a couple remote routers and Linux boxes I need to administrate. Rather than expose the router administration directly to the internet, I typically forward a port from a Linux box for SSH and then use a SOCKS5 proxy to get to the router from behind the firewall. So it's something like this:

• Router (WAN IP 1.2.3.4, LAN IP 192.168.0.1) is configured to forward 192.168.0.100:22 to port 2222
• I SSH (using Putty for Windows) to 1.2.3.4:2222
• Putty is configured to tunnel port 9999 dynamically (SOCKS proxy)
• I configure my browser to use a SOCKS5 proxy on 127.0.0.1:9999
• I point my browser to 192.168.0.1, and I get the router's administration screen

The Linux server is configured to only allow access via SSH keys, so it's hardened compared to the typical router's basic auth. This mostly works great, except for one particular router when accessed by Chrome.

Using the same basic setup described above, Router1 (running up-to-date open-source firmware) works fine from both Chrome and Firefox. Router2 (running obsolete Netgear firmware) works fine with Firefox, but with Chrome I get:

This page isn’t working 
192.168.0.1 sent an invalid response.
ERR_INVALID_HTTP_RESPONSE

When I'm physically on site (behind Router2's firewall) I can access it with Chrome just fine. The same is true if I (temporarily) enable remote management. So there seems to be something about the Netgear firmware that Chrome doesn't like when accessed via proxy.

This seems to be a relatively recent change in Chrome, because Router2 used to work over the proxy with Chrome. (Current Chrome in use is Version 75.0.3770.100 (Official Build) (64-bit) on Windows.)

I can't see anything useful using Chrome's Developer Tools (although I'm not very proficient at that).

How can I get this to work in Chrome, or at least figure out what's going on?