ST4 schema no longer functions with Studio 2019

I have recently upgraded to Studio 2019 on my laptop.

The XML (ST4 schema) files are no longer converted correctly, although this worked once!

I have tried importing several XML (ST4 schema) files that were converted correctly with Studio 2017 - they are always converted as XML: Any v 1.2.0 even though I have deactivated the associated checkbox! Does anyone have an explanation for this behavior? 

PS I have reimported the ST4 settings and double-checked that they are activated.