Meaning of "Couldn't fetch mysqli_result" ?

[tellmethis]

I currently have an installation of phpBB 3.3.10, which is hosted on what I think must be a Linux virtual server running PHP 7.3.23.

When a user navigates to the UCP, this displays in the top left of the browser window:

Code: Select all

[phpBB Debug] PHP Warning: in file [ROOT]/phpbb/db/driver/mysqli.php on line 264: mysqli_fetch_assoc(): Couldn't fetch mysqli_result
[phpBB Debug] PHP Warning: in file [ROOT]/phpbb/db/driver/mysqli.php on line 326: mysqli_free_result(): Couldn't fetch mysqli_result

The display of this PHP warning itself doesn't prevent a user seeing the UCP. However the problem was noticed when a user tried to navigate to Manage Attachments, at which point a blank page is returned.

I don't know whether it's a clue as to the cause, however whatever steps the server host took to rectify a problem reported via What's the meaning and effect of open_basedir ?, the steps included:

It seems that the PHP version is changed from 7.4 to 7.3. We have updated the php version from php7.3 to 7.4 and the website start loading fine.

Any clues as to where to begin to fix this new issue

Any tips welcome. Many thanks.