Moodle LMS expert Issue Resolution

Our Moodle 5.x site generally runs well, yet three stubborn problems keep coming back and I have run out of ideas:

– Teachers see a blank or broken page when opening the submission screen for one particular assignment, while the same page loads fine for me as Admin.
– Quiz grading calculates perfectly for every learner except one; that single attempt refuses to finalize no matter how many re-grades I trigger.
– One course instructor receives an “exception” message any time she clicks “Add activity or resource”.

All of these issues appear randomly rather than after an update or a predictable action. I have already cleared caches and double-checked role permissions, but neither step helped. If deeper server-side access or log files are required I can request temporary SSH / cPanel credentials from the hosting team.

What I need from you:
• Diagnose the root cause of the three errors and explain it in plain language.
• Apply fixes (PHP, database, permissions, or plugin conflicts) directly in Moodle so the pages load and grade correctly.
• Provide a brief report of steps taken so I can repeat them if the problem re-emerges.

Acceptance criteria: teachers can open the assignment submission page, the outlier quiz attempt receives its correct grade, and the instructor can add activities without exceptions.

You will be working with full Admin privileges inside Moodle and connect remotely with me; let me know if you also need server access or version information on PHP/MySQL.