Specific subdir won't show any files unless fileid is specified

I am running debian stretch 9.5, NextCloud 14.0.3 on Apache 2.4.25 , PHP 7.0.32
The system has <10 users and is running 99.999% - just this one little weirdness.

The symptom is similar to Not all files show under a specific folder.
Based on the links in that post and Problem upgrading from 12.0.3 to 12.0.4 (utf8mb4) - I have checked file permissions, as well as DB parameters and all seems fine/correct.

Any subdir that I access has files/subdir visible, but one particular one just shows a spinner and a blank filelist screen - like this

I looked in the oc_filecache table and found a few relevant fileids. If I use those specifically in a URL like this
or like this
then it displays the list of files perfectly, but if I click the parent subdir link, it shows just the spinner.

In the nextcloud-access.log I have a status 207 - - [08/Nov/2018:15:22:23 +0200] “PROPFIND /remote.php/dav/files/user/Documents/%5B_suppliers_%5D/Supplier%20Name HTTP/1.1” 207 28334 “-” “Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.132 Safari/537.36”
but I can’t find an explanation for that (here). This page indicates that it is a “Multi-Status” error, but I don;t know what that means or how to fix it.

There are no fancy characters in the file/subdir names.
This is not a critical problem - just wondering if anyone has seen/solved anything like it.