I felt it was necessary to create a thread about this subject as this is an old mesh issue that sadly seems to have been glossed over in the bug reports. If you play Fallout 4 in the third person and use power armour, it's a visual problem that is almost impossible to ignore because of how ugly it is.
When the player wears an outfit that is not a Vault Suit and enters power armour, the gear you're wearing will change to a set of Road Leathers. This outfit has horrendous clipping problems at the rear of the power armour frame's shoulders during the walking, jogging and run cycles without any weapons equipped.
I must stress that this issue doesn't occur when wearing a Vault Suit. That outfit retains its mesh underneath the power armour frame; this is exclusively a problem when wearing any other set of clothes.
I'd be super appreciative if this problem were rectified in a future UF4P release. It's a mesh issue that has been fixed by other individual mods (Example 1 - Example 2), but I feel it's something that should be included in the Unofficial Patch.