Operating system: Windows-10-10.0.17763 64 Bits
Graphics card: Intel(R) UHD Graphics 630 Intel 4.5.0 - Build 220.127.116.1111
Broken: version: 2.80 (sub 74), branch: master, commit date: 2019-06-26 19:03, hash: rB155c62b070a9
When the object (tentacles) is parented to the main body the normals seems to be okay - all blue (viewing it using face orientation checkbox)
but when you join them together only the tentacles get their normals flipped to red.
the problem is that on my headset it looked like backface is on but i couldn't see it in blender because all the normals were in the same direction (blue).
attaching .blend file for your review.
as I am not sure how to reproduce the situation.