Rebooted, flashed with settings kept. No luci HTTPS when booted and password auth failed, but ssh worked with key auth.
Installed missing packages, rebooted and when booted there was no luci - HTTP or HTTPS. Login in with ssh, enabled and (re)started uhttpd and luci was back with working password auth.
Everything I've checked so far in addition to wired and wireless functions seems to be working fine: HE.net 6in4 tunnel, DDNS, USM drive with btrfs, minidlna, haproxy, ZNC.
Looks like there are well over 100 devices on the Ralink rt305x target. The Table of Hardware is a great place to find out what the current support is for a device.
If you don't find what you're looking for there or on the wiki (such as downloads.openwrt.org or using the build system), perhaps a thread in the Hardware Questions and Recommendations or the For Developers section (if you're wanting to port to a new device) would be a good plan.
Maybe this is just part of x86_64 but thought it worth asking. Am playing with the x86_64 version in Libvirt / QEMU to build a secure partitioned off set of VMs. Gave it 64MB, which would be enough for a real router. Nope, opkg wouldn't work. 96MB will get it to work on the command line but 128M was needed to get package management in luci to work. Seems a mite excessive.
Have 18.06.1 on a D-Link DIR 825 (Atheros mips32) with only 64MB and everything is is full of winning. Is this just the price of running 64 bit code? Would it be better to swap out for one of the plain x86 versions?
The web page for the BT Home Hub 5 is still pointing at the v18.06.1 version (linked 15th June 2019 and I have a suspicion that a lot of pages are on this site are using outdated methods, links and instructions.
"Hard links" to OpenWrt releases are generally discouraged, unless it's a case of, for example, "you must use this, specific one to flash from OEM."
I see that the page you linked has some "historic" information on it, but the most-current should be from the auto-generated table, that typically looks like
There's been changes on the page since I mentioned the apparent problem, and there are links to an 18.06.2 download, but my eyes aren't good enough to be sure that anything on that page matches your example. It does look like somebody woke up, but I can't be sure.