Could you please share the whole trace? The problem is not that we display HTML tags, but the content we put into that alert. This is 500 response, which seems to be specific to your env. It says unsupportes browser, so I wonder what do you use :-)

if you actually look, you would see its a full page response, including the warning about the browser (which exists in every page foreman providers).
the actual error is provision template not found

Ah, sorry I read just part of that HTML (on phone). I can't reproduce on develop though, does that happen for all templates you have? Could you upload the log from the server with debug log level? Thanks