I just saw someone post a similar issue about xwiki timeouts (https://forum.xwiki.org/t/incessant-timeouts-slow-performance-overall/3595)
So I installed javamelody on the server to monitor the usage of the service, seeing that there is a high consumption of the CPU around 200%.
On the post they say the notification system has some issues about high comsuption of CPU, so I decide to disable the notifications using the documentation on this page https://extensions.xwiki.org/xwiki/bin/view/Extension/Notifications%20Application/
After disable the notifications the cpu usage drastically drops to low levels.