Hello Alvaro
That’s interesting. Normally, when you reinstate the summary-address command, the summary address should appear in the RIP neighbor. Take a look at this text from a Cisco Document (link below).
As long as there are child routes for a summary address, the address remains in the routing database. When the last child route is removed, the summary entry also is removed from the database. This method of handling database entries reduces the number of entries in the database because each child route is not listed in an entry, and the aggregate entry itself is removed when there are no longer any valid child routes for it.
The only reason that a summary will not appear is if there are no child routes remaining in the local router, that is, there are no routes that fall within that summary. Here is the link from where this text was found. This Cisco document further describes route summarization and may be of help to you.
What I suggest is to examine, if you remove the summary-address command, do you see the individual routes that fall under that summary being advertised? If not, then this is the reason why the summary is also not advertised. If however they are there, then you should check to see if there is an error anywhere else in the configuration that may be causing this.
I hope this gives you some help in continuing your troubleshooting.
I hope this has been helpful!
Laz