Achievement didn't unlock for me after I collected the last two.
I viewed all the artefacts, made sure I collected the right ones, looked at a couple of videos, walked all the upper branch areas again to make sure I didn't miss any, but nothing.
I continued to the next chapter with the spider legs and then quit to main menu.
Picked continue and then went to page 3 of the checkpoints and selected the first one. Once it loaded the achievement popped right away.