I updated from 4.5.5 to 4.5.7 today (“keep settings” enabled), after, login to GL-inet-GUI was impossible (http://192.168.8.1 was redirected to http://192.168.8.1/cgi-bin/luci).
Luckily I had backed up my config and after restoring it login to GL-inet-GUI was possible.
I also faced the redirect error when logging in to LuCi from HTTP*-GL-inet-GUI, firmware should not link to 192.168.8.1/cgi-bin/luci but https:// 192.168.8.1/cgi-bin/luci (pls ignore the space after https://)
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*no S here, the plaintext, unencrypted access to GUI