> carrier grade NAT (CGNAT), which is used by ISPs that have run out of IPv4 addresses … If you’re unlucky enough to be on one of thee ISPs there’s likely not much you can do.

I had the same SSH dropout problem, asked my ISP[1] to switch me from CGNAT to dedicated IPv4; they did, and it's fixed.

[1] Aussie Broadband, a smaller ISP in Australia renowned for good customer service.