Luci fails to start, openwrt_s905x3_k5.4.158_2021.11.12.1717

Fresh install of OpenWRT 21.02.1 on an X96 Air Android TV box. OpenWRT running on USB stick. Accessing the web interface gives a Bad Gateway error. Running /www/cgi-bin-luci over ssh results in the following:

root@OpenWrt:~# /www/cgi-bin/luci
/usr/bin/lua: /www/cgi-bin/luci:4: attempt to index field 'dispatcher' (a nil value)
stack traceback:
        /www/cgi-bin/luci:4: in main chunk

The luci script is simply:

root@OpenWrt:~# cat /www/cgi-bin/luci
#!/usr/bin/lua
require "luci.cacheloader"
require "luci.sgi.cgi"
luci.dispatcher.indexcache = "/tmp/luci-indexcache"
luci.sgi.cgi.run()

---------- I've tried creating an empty directory /tmp/luci-indexcache with no difference to the result. Deleting it again also makes no difference. I suspect there may be an issue with luci.cacheloader, but I don't know where to find it, or whether it is text or binary. I have *no* Lua experience. Googling doesn't return anything that looks like a solution. Is anyone able to help me out please?