As mentioned elsewhere, this will be fixed as part of the work for Multiple users and groups in snaps. This work is on the roadmap but not prioritized. To help out, I’m working on this in the background so while it is progressing, it is progressing slowly. Note that chown to root:root is currently allowed.
In the meantime applications can either be patched to not perform the chown or use the snapcraft preload part: https://github.com/sergiusens/snapcraft-preload.