Can't cause damage to enemies

I need some help. I haven’t played Grim Dawn in a while and right now I’m stuck. I’m located north-east of Blood Grove probably near Village of Darkvale. Everything was working fine, and then I got into an area where I can’t cause damage to certain enemies. A red Pentacle appears over my head and I can’t cause any damage. Eventually I can damage some enemies but not others and then another red Pentacle appears over my head and I can do nothing. I tried for a long time but eventually just gave up as I cannot progress in the game. Could someone please explain the ‘no damage’ issue and what the red Pentacle is for?

I have never experienced this issue. On which difficulty are you? Are there Hero mobs or Harbingers around? Please also link your build.