The map appears as a grey rectangle with the text "Loading map..." (potentially translated)

Cannot reproduce in Firefox 82 on the web page that you linked. Please provide clearer instructions.

Please provide clearer instructions.

This is my screenshot with Firefox 82.0.2:

The console prints the following warnings:

• Use of "mobile.init/skin" is deprecated. Use instance of mobile.startup/Skin. Minerva should have no dependencies on mobile.init instead.
• Use of "getCurrentPage" is deprecated.

I repeated the setup after signing out and it resulted in the same output.

Seeing the same thing with Chrome 86.0.4240.75 (Official Build) (64-bit) on Linux (Debian).

console shows the following:

[0d21d5c3beb5ea12a7503869] 2020-11-02 13:18:50: Fatal exception of type "InvalidArgumentException"
[0d21d5c3beb5ea12a7503869] 2020-11-02 13:18:50: Fatal exception of type "InvalidArgumentException"
[0d21d5c3beb5ea12a7503869] 2020-11-02 13:18:50: Fatal exception of type "InvalidArgumentException"
[0d21d5c3beb5ea12a7503869] 2020-11-02 13:18:50: Fatal exception of type "InvalidArgumentException"

Problematic modules: {"startup":"error"}
(anonymous) @ load.php?lang=en-gb&modules=startup&only=scripts&raw=1&skin=vector:12

Please also check the network tab (not only the console tab) for any HTTP 4xx or 5xx errors or items which load very slowly.

@donal.hunt: If there are startup errors, could you pelase follow https://www.mediawiki.org/wiki/Help:Locating_broken_scripts and use debug=true for better URLs?

Thanks everyone!

@Aklapper I only get 200s. https://wiki.openstreetmap.org/w/load.php?lang=en&modules=startup&only=scripts&raw=1&skin=minerva&target=mobile seems to be rather slow (510 - 640 ms). Sorry, I do not know what this script does or if it is based on some special page, otherwise I would have noted it here, too.

Your screenshot shows a blue shield in the top left corner. Does it block a script on this page?

Anyone who can reproduce this problem please open a tab in your browser, open the network tab of your browser's developer tools, go to https://wiki.openstreetmap.org/w/index.php?title=User:Tigerfell/Sandbox&oldid=2054479&debug=true (note the debug=true), and check for errors. Thanks.

In T266654#6642529, @FellTiger wrote:

Your screenshot shows a blue shield in the top left corner. Does it block a script on this page?

I don't think so, how could I find out? (And even if, I'd guess it should rather be the other way round that something does not work if I blocked something? :) )

This can be reproduced with a throttled network. "Loading map..." and grey rectangle will appear momentarily before the map fully manifests. but the task as written is invalid as this cannot be fixed in Minerva or may be even MultiMaps. The "Loading map.." text is apparently intentionally there to tell way something is on the way.

I tried to replicate the issue last night and was unable to reproduce it. That doesn't mean there wasn't any issue originally though.

@Aklapper wrote:

Anyone who can reproduce this problem please open a tab in your browser, open the network tab of your browser's developer tools, go to https://wiki.openstreetmap.org/w/index.php?title=User:Tigerfell/Sandbox&oldid=2054479&debug=true (note the debug=true), and check for errors. Thanks.

The images resembling the map are available from subdomains of tile.openstreetmap.org. There seem to be no requests to this address when using Minerva Neue skin.

I don't think so, how could I find out? (And even if, I'd guess it should rather be the other way round that something does not work if I blocked something? :) )

If you click on the blue shield, your browser will tell you what it blocked.

No, the result is the same. Continuous map loading with the "Loading map" display.