Hi Renzo,
Any particular activity is not showing or old activities is not showing.
By default system will show only 100 documents and we can set the time frame in the below configuration. you can check for the time frame.
Transaction SPRO ->IMG -> Customer Relationship Management -> Master Data -> Business Partner -> Specify Display Options for Business Transactions.
If any particular activity type is not seen then check Data Retrieval Parameters as per note 1860898.
With regards,
Selvam