1. Siquence diagrams are failing on messages which are on one line ao more than 901 characters (even if it's splitted with \n)
2. Following the hint from
https://forum.plantuml.net/3104/sequence-diagram-messages-on-multiple-lines ...
Splitting the line with "\" it helps a bit, but if the complete line (including those merged by "\") eceeds 2013 characters, the participants are automaticaly tranformed into classes and the text is justified aligned.
Example: //www.plantuml.com/plantuml/png/SoWkIImgAStDuN9qTDIrKt020Yi5coGxc-JydFmYAsMddD9KEmNVrEBYnFHK2gcOl9WIKbHZ5QQnKuQLdPWke6MuqzyxN6GvcVxnFBn2FGyUxXHI8oq3Ohfdw0L4J1wDid9C7d7gKga5OhXAS8EOl19QW1YkT2g3Kdm0egIoCeJB8JKl1LZB0m00