Error to view and write to the database Moodle 3.9.5+ (Build: 20210312)

[hr-curtissimo]

Environment:

• Moodle 3.9.5+ (Build: 20210312)
• PostgreSQL 11.10 (Debian 11.10-0+deb10u1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 8.3.0-6) 8.3.0, 64-bit
• Additional plugins (all installed from Moodle Plugins directory, except where noted)
  • Edumy theme (installed manually)
  • Restriction by relative date
  • Restriction by course completion
  • Level up!
  • Grade Me
  • Custom certificate
  • BigBlueButtonBN
  • Attendance

Steps to Reproduce

• I installed this plugin from the Moodle Plugins Directory using the Install button.
• The first cache_grade_data task completed successfully.
• I added the block to my dashboard.
• I saw "Nothing to grade" when there should be something.
• I used the "Refresh quiz" link on the block configuration page.
• I saw "Nothing to grade", still.
• The content of the log for the task shows this message:

Execute scheduled task: Grade Me (block_grade_me\task\cache_grade_data)
... started 09:48:01. Current memory use 19.6MB.
... used 11 dbqueries
... used 0.035485029220581 seconds
Scheduled task failed: Grade Me (block_grade_me\task\cache_grade_data),Error reading from database