For some reason, removing either of the two templates at the top of the page eliminates the Linter error.

Expanding either of those templates {{Map of heritage railways in Great Britain}} in https://en.wikipedia.org/wiki/Special:ExpandTemplates shows an exceedingly large mapframe,

<mapframe text="Interactive map of standard gauge heritage railways in Great Britain." latitude="53.958333" longitude="-1.080278" zoom="5" width="300" height="300" align="right">
{
  "type": "FeatureCollection",
  "generator": "overpass-ide",
  ...

Stacking two of them together is going to run afoul of the wikitext size limit in Parsoid, 'wikitextSize' => 2048 * 1024, // ParserOptions::maxIncludeSize
https://github.com/wikimedia/parsoid/blob/master/src/Config/SiteConfig.php#L1661-L1662

Once that's hit, templates will no longer be expanded,
https://github.com/wikimedia/parsoid/blob/master/src/Wt2Html/TT/TemplateHandler.php#L1005-L1023

so from [[File:Craignure Station.jpg|thumb|right|Craignure station on the {{nowrap|10.25in}} gauge Isle of Mull railway]], the | in {{nowrap|10.25in}} will be interpreted as a file option delineator and you'll get two captions, Craignure station on the {{nowrap and 10.25in}} gauge Isle of Mull railway. Since the last one wins, the former is noted as,

{"type":"bogus-image-options","dsr":[0,113,2,2],"params":{"items":["Craignure station on the {{nowrap"]}}

Note that in https://en.wikipedia.org/api/rest_v1/page/html/User:Jonesey95%2Fsandbox/1032656599, we have,

wt2html: wikitextSize limit exceeded

The difference in limits between the parsers is tracked in tasks like, T254522 / T254508