In T407043#11810331, @Harryboyles wrote:

So I have been debugging this as I have the exact same issue - hopefully this will help developers to find a proper fix

Within WikiFunctions.Parse.Parsers.Templates, the use of GetAllTemplatesDetailNewQueue to cache template details appears to be the location of the issue. I've found that when the method public static List<string> GetAllTemplateDetail(string articleText) is called a second time, the GetAllTemplatesDetailNewQueue[n].Value string List associated with the cached article text is cleared and is an empty list instead of being the list of template details. So this effectively means that there are "no templates" to evaluate child find/replace rules -> unless there is exactly one in-template call and it is the first time that the particular wikitext has been evaluated.

Interestingly, GetAllTemplatesNewQueue (the list of found template names) is not affected and that string list remains upon subsequent invocations.

In my own local build as a workaround I disabled the use of the GetAllTemplatesDetailNewQueue cache (by commenting out the if (found != null) return found conditional and force it to recalculate the templates every time, and now find/replace within in-template calls works like it should.

So I have been debugging this as I have the exact same issue - hopefully this will help developers to find a proper fix