Users getting "No access" message when they have access

Hi all, multiple users have raised an odd issue that I’m struggling to fix.

The workflow looks like this:

1. User browses to a page, to which they have Full access (the page itself differs for different users, across different functions).
2. They see the “No access. Your system administrator has not granted permission to complete that action” popup.
3. They click the ‘Close’ button. 
4. The message disappears, and they can do whatever they need to do.

[System: IFS Cloud, 23R2]

I’ve seen this post:

but our users already have FND_WEBENDUSER_MAIN, and always have had. Is there another reason why this issue might be occurring?

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Note: I’ve also seen this post:

and users don’t have the FndTempLobStore or DefaultInfo permissions. But nor do I, and I don’t experience these issues; and generally, that post looks like it might be a bit out of date now(?)