All share links lost on temporarily disconnected NFS external storage

Nextcloud version: 20.0.7
Operating system and version: Ubuntu 18.04.4
Apache or nginx version: Apache 2.4.29
PHP version: 7.2.24

Almost all of the data in my Nextcloud instance (virtual machine running on ESX) is an External Storage, which is an NFS mountpoint. Has been working well.

Yesterday, both my NFS server and Nextcloud instance were restarted for planned maintenance. It appears that Nextcloud started before the DNS server that resolves the NFS server’s name, so the NFS mount failed, and Nextcloud wasn’t showing any files.

A ‘mount -a’ at the console brought the NFS mount back, and the files reappeared shortly after in Nextcloud with no further tinkering.

But all the shares (share link URLs) are gone. Nothing is shared anymore.

A reboot of Nextcloud didn’t bring them back.

What’d be the best way to restore the shares? And more importantly - what happened and how (aside from ensuring that the NFS mount is always available, which may not be practical) can I ensure that this doesn’t happen again?

I didn’t answer the remaining questions in this form because there either isn’t any useful info (admin logfile) or no relevance (my config file).

Any help greatly appreciated!