A recent support discussion may have found a bug relating to importing into Affinity Publisher an svg file made using Affinity Publisher.
Could you have a look at the source software in Affinity Publisher that relates to this please?
1. 1.8.3.641
2. Yes.
3. Yes.
4. The following thread and a thread linked from it are relevant. https://forum.affinity.serif.com/index.php?/topic/117718-at-what-size-is-a-placed-svg-file-placed-please/
William