Don’t know about online servers, but all of those along the years are duplicates:
Sep 2017: https://steamcommunity.com/app/440900/discussions/0/1495615865209797037/
May 2018: Hoar-Frost Hatchet not harvesting
May 2018: https://steamcommunity.com/app/440900/discussions/0/2561864094356572583/
April 2018: Aiming problem with weapons and tools! Can be a serious bug!
April 2018: https://steamcommunity.com/app/440900/discussions/0/3288067088112126479/
Jun 2018: https://steamcommunity.com/app/440900/discussions/0/1728701877448871246/
Nov 2018: https://www.reddit.com/r/ConanExiles/comments/9ugmt0/cannot_hit_smaller_creatures_is_there_a_fix_for/
All posts say something about one weapon, but in fact is all of them. Besides the suicide to fix the issue seems that regenerate the character using the mirror from CharEditLite work too as a better fix.
Just to clarify how old is this bug, let me quote kirag-ig from Steam in 21/Sep/2017: “It’s brand new bug since yesterday patch. You cannot hit up or down with any weapons (…), only straight forward. Relogging is only way I’ve found to fix it.”
EDIT: found one about MP here in this forum (sadly, way more detailed post and with a similar “taking this back to the team to get some input” answer) Aiming problem with weapons and tools! Can be a serious bug!