New install: Log in to Dashboard returns "Something Went Wrong" error (full error message included).

Hi, I'm trying to get Vanilla setup on my server... Getting there, but it's a battle ;-)

I've got the frontend working fine, but when I try to login to the dashboard I get the generic "Something Went Wrong" error. I've added the required line to the config.php and I can see the following message...

The error occurred on or near: /home/caffeine/public_html/vanilla/library/core/functions.general.php

4058:         // replace non letter or digits by -
4059:         $text = preg_replace('/[^\pL\d]+/u', '-', $text);
4060: 
4061:         // transliterate
4062:         $text = iconv('utf-8', 'us-ascii//TRANSLIT', $text);
4063: 
4064:         // remove unwanted characters
4065:         $text = preg_replace('/[^-\w]+/', '', $text);
4066: 

Backtrace:

[/home/caffeine/public_html/vanilla/library/core/class.form.php:795] PHP::slugify();
[/home/caffeine/public_html/vanilla/applications/dashboard/views/modules/configuration.php:84] Gdn_Form->imageUploadPreview();
[/home/caffeine/public_html/vanilla/library/core/class.module.php:130] PHP::include();
[/home/caffeine/public_html/vanilla/library/core/class.module.php:281] Gdn_Module->fetchView();
[/home/caffeine/public_html/vanilla/library/core/class.module.php:258] Gdn_Module->toString();
[/home/caffeine/public_html/vanilla/applications/dashboard/views/settings/branding.php:9] Gdn_Module->render();
[/home/caffeine/public_html/vanilla/library/core/class.controller.php:782] PHP::include();
[/home/caffeine/public_html/vanilla/library/core/class.controller.php:1386] Gdn_Controller->fetchView();
[/home/caffeine/public_html/vanilla/library/core/class.pluggable.php:217] Gdn_Controller->xRender();
[/home/caffeine/public_html/vanilla/applications/dashboard/controllers/class.settingscontroller.php:560] Gdn_Pluggable->__call();
[/home/caffeine/public_html/vanilla/library/core/class.dispatcher.php:872] SettingsController->branding();
[/home/caffeine/public_html/vanilla/library/core/class.dispatcher.php:289] Gdn_Dispatcher->dispatchController();
[/home/caffeine/public_html/vanilla/index.php:29] Gdn_Dispatcher->dispatch();

Screenshot of the above...

V3.3. PHP7.3. From what I can tell all other dependancies are fine.

I'm working on my VPS and getting this issue. I've previously tested it on my test server, some cheap shared space, and it's all working fine!

I've tried installing from Softalicious and uploading the code manually, both times I hit this issue.

I've now run out of skill with stuff like this, can anyone offer any help?

Thanks.