Here is an instance where all picks, arrivals, amplitudes, magnitudes,... were lost during the conversion from Seiscomp3ML to QuakeML. I can't attach the xml files but here is what I entered in the browser line:
https://service.geonet.org.nz/fdsnws/event/1/query?eventid=2019p431888
http://seiscompml07.s3-website-ap-southeast-2.amazonaws.com/2019p431888.xml