#22 Error after cache is being populated

[Anonymous]

So recently we started to get this error:

HTML::Template::param() : attempt to set parameter 'page_title' with a scalar - parameter is not a TMPL_VAR! at src/modules/Chirpy/UI/WebApp.pm line 772

The error goes away if we clear the cache, but as soon as we refresh the page again, we get this error again. Any ideas what could be wrong?