Having made enquiries on the Microsoft community and on a thread here, I reached the conclusion that Flarum does not appear to offer full support for Windows 10 mobile.
I can access a post, but I'm only able to scroll a short way down and all the navigation aids are missing together with the '>click to reveal' spoiler tags.
An error message header states 'Something went wrong while trying to load the full version of this site. Try hard-refreshing this page to fix the error.'
Does anybody know how to 'hard-refresh' a Lumia 550 by any chance?
It has been suggested on giffgaff gd that Microsoft Edge has Internet Explorer 'compatibility mode' built in and this may upset the loading of some websites.
I must report that so far I have found no options in Microsoft Edge settings or anywhere else in the menu to switch off this option.
It makes no difference using the giffgaff app.
Any ideas, suggestions would be appreciated.