We have held an online exam with Lockdown Browser today, which involves about 300 students. At the 15 minutes before the exam end time, a lot of students uploaded answer photos to Moodle. Afterwards, Moodle becomes very slow and most students cannot be even login. Some students encounter the error messages of "504 Gateway Timeout".
After the exam, we have already restarted the Moodle. It is strange that almost 32 vCPU are having 80~95% loading. It should not be used by a lot of students at this moment.
Please advise what's happening on the Moodle. Kindly advise how to fix this problem. Thank you very much.