I have same issue, started 2020.11.28, people are physically present in system but does not appear in local. Doesn’t matter if it’s hsec, lowsec or nullsec, probably may happen for any system in the game. I am providing two screenshots, one with two people in local including me, but can see 3 on dscan. And second one with me sitting in same NPC station as guests with another player which does not appear on local chat.
I can provide not cut, full screenshots for members of CCP team, please investigate this further, fly safe pilots! =)