Hi PedroN,
there are several causes, which might result in a non-working link for "...:8443/admin/update/product/" ( which is a redirect to "...:8447/summary.html ).
Consider to post log - entries from your panel - log, inspect your firewall settings, ckeck for dublicate "autoinstaller" - instances ( or/and "hanging" process(es) ), investigate possible hanging process(es) with for example "strace", restart the services "psa", "sw-cp-server" and "sw-engine", check if the services "sw-cp-server" and "sw-engine" are in a working state, check with "netstat", if the port "8447" is opened, when you tried to opene the "Updates and Upgrades" - site.
Further investigations can not be done without MORE informations from the corresponding log - files.