Hello Teseo,
As you suggested, it works now perfectly with FcgidBusyTimeout.
For those who might be interested in the future, the link provided by teseo is very useful. However, I did it directly through Plesk panel. In the domain setting, go to Apache & Nginx settings and in the section Additional Apache Directives I added the following in "Additional directives for HTTP" and "Additional directives for HTTPS":
FcgidIOTimeout 6000
FcgidBusyTimeout 6000
You then change the seconds you want to configure the timeout with.