XSweet conversion error
There is both a positive response and a negative response HTML output from xsweet container.
In the negative response; we don't get an HTML output from xsweet container it fails with a 500 error and does not provide any HTML response this is happening with the above file you have shared. The problem does not seem to be at kotahi end it's happening at xsweet for some reason and I don't have enough info to debug from the xsweet container logs which just show the 200 succeeded response and 500 failed response.
The positive response; When running the manuscripts through http://demo.xsweet.org/ the conversion appears to be successful.