Thanks all for your comments.
I think that I have identified the problem and some kind of work-arround to solve it.
I'd try to explain while answering your comments back:
1) No, it is not a typo. Actually, to make a test, I let cakewalk rendering the mix of "what I supposed to be a 3 minutes length" to a wav file at Monday, 22.00 and next day by 20.00 it haven't ended yet...
2) Then, I wrote to firstname.lastname@example.org telling about my issue and quite quickly they asnwered back (lit): "Thanks for reaching out. So sorry for the trouble. We are in the midst of investigating all the bugs reported so far with the new update and working to release a new hotfix for it soon. For now, please revert back to version 2021.01 by running the rollback installer". And so I did: rolled back the update, but the problem wasn't solved
3) Finally, as both Noel and scool said, I made the Export Module visible in the modules bar (I use to work on a Surface so I usually have most of the modules hidden due to lack of space in my screen) and, surprise: what was supposed to be a 3 minutes length project, actually is 08:26:41:14!!!!!!!
So, easy way to have the project's mix rendered to a file is just selecting the section that you want to export and voilá!, mix is renderd in less than half a minute.
Now, my question is: I've been using cakewalk for almost 20 years... (since it was named Cakewalk Pro Audio v6, before SONAR1...) and I can't remember a single time I've had to worry about selecting the length of the project before rendering it (as usually happens with other DAWs such as ProTools or Logic) so why is it now happening that Cakewalk is extending the project duration so much?
I haven't been able to find out any event by the end of the last recorded data...
Hope this helps.
Thanks again for you comments.