Comic Sans is a system font on many operating systems, but not all.

It might be that your mobile client singlehandedly does not have it and replaces it with something different of the same category. That being said - Comic Sans is considered one of the worst fonts for webdesign and usually not used at all.

I've found some span classes on the page that refer to it, so it is reasonable that it is displayed.

If you want to be sure the site is displayed on all devices equally you either need to use a widespread system font like Arial or Helvetica or implement a Webfont from one of many sources (google webfonts being popular), which you can host yourself (for privacy/GDPR reasons) or use their service (for ease of use).