Please check your logfile at var/log/prod.log. Many problems reveal themselves after checking it.
If that doesn’t help, open a new discussion at GitHub and we try to find a solution. Please include the last ~ 20-50 lines of the log file, which were written around the time the error happened.
There are many factors that influence the performance of Kimai, the most important one is the server Kimai runs on. Shared hosts aren’t known for their good performance, especially running modern PHP projects like Kimai that load a large amount of files per request.
The second factor is your PHP configuration, which can lead to massively decreased performance when not tuned for production usage.
Please read this issue.
Kimai is built on top of Symfony, a framework that optimizes its speed by caching most files.
Therefor, if you are running Kimai in production, you have to clear the cache before changes will show up.
Sorry, no chance. You either have to find a hoster that offers SSH access, or you use the SaaS version of Kimai.