Failure to complete Let's Encrypt renewal process

I'm having a strange Let's Encrypt issue:

Failed to request certificate : Cannot write to directory /var/cache/bind/

The cert renewal itself completes, and the cert files are copied to /home/username/ssl.cert etc. But the Apache reload is not done and then I get the above error. If I manually reload Apache the site loads with the new cert.

I've tracked this down this problem to open_tempfile_as_domain_user() in /usr/share/webmin/virtual-server/ but I can't figure out the call chain. This is the only function in the entire codebase that can print "Cannot write to directory".

Virtualmin version: 
Webmin version: 


I see the cause of this - it will be fixed in the next Webmin release.

FYI, this problem recurred under Virtualmin 6.13.gpl on Ubuntu 18.04.5 LTS.

We just released version 6.14 - if you upgrade, do you still see this issue?

This was fixed under v6.14 and v6.15, but has now recurred under v6.16 (upgraded recently).