Local font not displaying on mobile

Hi team

I have a local font set up, League Gothic (from Font Squirrel), in use for all headings on the site. It's working as intended on MacOS in various different browsers (tested on 2 Macs), but not on Win10 (Firefox and Edge) and not on iOS (Firefox and Safari) - the Inspector reveals the font name is being called correctly but it displays as a sans-serif fallback, though weirdly the main page headings are displaying as sans-serif but a thin one, not League Gothic. I've searched the forum and checked and re-checked the code, cleared browser caches etc.

This is what I have for CSS (the font name is as specified by Font Squirrel):

/* Custom font */
@font-face {
    font-family: 'league_gothicregular';
    src: url('https://DOMAIN/wp-content/uploads/2021/06/leaguegothic-regular-webfont.eot');
    src: local('League Gothic'), local('league_gothicregular'),
		 url('https://DOMAIN/wp-content/uploads/2021/06/leaguegothic-regular-webfont.eot?#iefix') format('embedded-opentype'),
         url('https://DOMAIN/wp-content/uploads/2021/05/leaguegothic-regular-webfont.woff2') format('woff2'),
         url('https://DOMAIN/wp-content/uploads/2021/05/leaguegothic-regular-webfont.woff') format('woff'),
         url('https://DOMAIN/wp-content/uploads/2021/06/leaguegothic-regular-webfont.ttf') format('truetype');
    font-weight: normal;
    font-style: normal;
}

And this in functions.php:

/**
 * Add custom fonts (local, Typekit, Fonts.com, etc.) to local font list.
 * @link https://docs.generatepress.com/article/adding-local-fonts/
 */
add_filter( 'generate_typography_default_fonts', 'gpc_add_custom_local_fonts' );
function gpc_add_custom_local_fonts( $fonts ) {
    $fonts[] = 'League Gothic';
    return $fonts;
}

It's been working fine since the start of development (on a Mac), it shows up inthe customiser and generally behaves as expected. I only noticed the issue when I checked on my phone and old Win10 laptop once it was on a test server. What am I doing wrong? The site is still being developed so I'll send the URL privately (all caching currently disabled).