1) It depends. When the "hologram" appears, if in the scoreboard (TAB) the word "LAG" is only appearing in that specific player's name and not everyone then it's a problem from their end. If it says "LAG" for everyone then it's a problem from your end. These types of things are lag spikes; sudden losses/declines of internet stability (pj) between players. Also, when you get the "holograms" don't shoot at them, it won't do any effect. Furthermore, there's a slim chance that sometimes some players use these lag spikes as an advantage through lag hacks; you have to follow the patterns of when they lag and if you notice that they always seem to lag in specific moments such as when they have low health before dying, before getting the flag, etc. you might be talking about a lag hack.
2) You are most probably talking about the sniper@camper maps. All official maps (While in a server press ESC > Set mode/map > mode > list of official maps) don't have those kinds of invisible walls and holes that players can take advantage of next to the bases. Best thing you can do in those maps is get away from the base as soon as possible before they can get a shot at you, though I would recommend you play official maps online and see if you prefer it.
Hope this was helpful and welcome.
2) You are most probably talking about the sniper@camper maps. All official maps (While in a server press ESC > Set mode/map > mode > list of official maps) don't have those kinds of invisible walls and holes that players can take advantage of next to the bases. Best thing you can do in those maps is get away from the base as soon as possible before they can get a shot at you, though I would recommend you play official maps online and see if you prefer it.
Hope this was helpful and welcome.