Some elements not loading

Hello,
We have recently grown our user base and added some large projects which makes for a heavy database.  Recently we have started to see occurrences of data not loading (or not displayed), rather randomly.  I have checked the logs on server and in browser, but there is no error seen at that time.
The only thing I see sometimes is some Mysql lock wait timeouts in the logs, but not necessarily when I see these display errors (that's another investigation).

Example attached : list of tickets is displayed, but ticket detail stays empty.

Have you ever seen anything similar or have an idea what could cause such behaviour ?
Thanks.