Hi all,
Thanks for your reports about this. We're aware of an issue that can prevent the temporary invulnerability effect from being applied in some situations after Fast Traveling or Respawning in Survival mode. We're actively investigating this and looking into a fix for a future update.
As a workaround, avoid fast traveling or respawning in locations where there have been lots of PVP-related player deaths (these areas will have multiple skull icons on the Map).