Hey Paolo,
Thanks for reaching out! This issue is likely resulting from plugin or theme code elsewhere on your site that is limiting the excerpt length…
Unfortunately, the only to find out the exact source is to run through the set of steps here → https://theeventscalendar.com/knowledgebase/testing-for-conflicts/
If you check on the event descriptions after EACH STEP in that process, let me know what you find! If you change themes and then the descriptions show up full length, for example, then your theme would be the source of the issue…and same if you deactivate other plugins and then the descriptions show up.
Let me know what you find!
Cheers,
George