Bug: Sort by "last modified" is not working

[v3DJG6GL]

Describe the bug

The Sort option "last modified" is not working.
When I change sort order to last modified and switch e.g. between All contacts and Not grouped, I get this error:

Unable to retrieve the contact from the server, please check your network connection.

If I refresh the page instead, Sort setting is reset to previous value.

Steps to reproduce

1. Go to Contacts in WebUI
2. Click on Contact settings
3. Set sort contacts to Last modified
4. Close settings and:
   4a. Switch between e.g. between All contacts and Not grouped and you'll see this error:

   Unable to retrieve the contact from the server, please check your network connection.`
   

   4b. Reload the site and the Sort settings will be reset to previous setting.

Expected behavior

Sort by last modified should work

Actual behavior

Sort by last modified is producing an error message and is not saved.

Contact version

v8.4.0

Operating system

TrueNAS SCALE 25.10

PHP engine version

PHP 8.4

Web server

Nginx

Database

PostgreSQL

Additional info

Nextcloud: v33.0.0

[GVodyanov]

Hey! Thanks for the report, I was able to reproduce it. If you feel like creating a PR for this we'll be happy to assist you.

[v3DJG6GL]

Hey! Thanks for the report, I was able to reproduce it. If you feel like creating a PR for this we'll be happy to assist you.

I've made an initial attempt to fix the issue, see this branch:
main...v3DJG6GL:contacts:fix/sort-by-last-modified-5158

There were several issues I had to fix to get last modified working correctly. Lots of my contacts seem to have no REV value set at all - and there seems to exist different types of formatting for REV like e.g.:

REV:20250624T112022Z
REV;VALUE=DATE-TIME:20260312T204000Z

So far it works on my end, but only with basic testings tbh...